There is yet no reason why God should not have extended the grace of the new covenant to the fathers. This is the true solution of the question.
Calvin taught that the Old Covenant and the New Covenant were both equally the eternal Covenant of Grace.
1. From what has been said above, it must now be clear, that all whom, from the beginning of the world, God adopted as his peculiar people, were taken into covenant with him on the same conditions, and under the same bond of doctrine, as ourselves; but as it is of no small importance to establish this point, I will here add it by way of appendix, and show, since the Fathers were partakers with us in the same inheritance, and hoped for a common salvation through the grace of the same Mediator, how far their condition in this respect was different from our own… The covenant made with all the fathers is so far from differing from ours in reality and substance, that it is altogether one and the same: still the administration differs.
The administration differs with regards to outward appearance, rather than to true substance.
the comparison made by the Apostle refers to the form rather than to the substance; for though God promised to them the same salvation which he at this day promises to us, yet neither the manner nor the character of the revelation is the same or equal to what we enjoy.
(Commentary on Hebrews 8:6)
Here we may see in what respect the legal is compared with the evangelical covenant, the ministry of Christ with that of Moses. If the comparison referred to the substance of the promises, there would be a great repugnance between the two covenants; but since the nature of the case leads to a different view, we must follow it in order to discover the truth. Let us, therefore bring forward the covenant which God once ratified as eternal and unending. Its completion, whereby it is fixed and ratified, is Christ. Till such completion takes place, the Lord, by Moses, prescribes ceremonies which are, as it were formal symbols of confirmation. The point brought under discussion was, Whether or not the ceremonies ordained in the Law behaved to give way to Christ. Although these were merely accidents of the covenant, or at least additions and appendages, and, as they are commonly called, accessories, yet because they were the means of administering it, the name of covenant is applied to them, just as is done in the case of other sacraments. Hence, in general, the Old Testament is the name given to the solemn method of confirming the covenant comprehended under ceremonies and sacrifices. Since there is nothing substantial in it, until we look beyond it, the Apostle contends that it behaved to be annulled and become antiquated (Heb. 7:22), to make room for Christ, the surety and mediator of a better covenant, by whom the eternal sanctification of the elect was once purchased, and the transgressions which remained under the Law wiped away. But if you prefer it, take it thus: the covenant of the Lord was old, because veiled by the shadowy and ineffectual observance of ceremonies; and it was therefore temporary, being, as it were in suspense until it received a firm and substantial confirmation. Then only did it become new and eternal when it was consecrated and established in the blood of Christ. Hence the Saviour, in giving the cup to his disciples in the last supper, calls it the cup of the new testament in his blood; intimating, that the covenant of God was truly realised, made new, and eternal, when it was sealed with his blood.
He contends that Hebrews 8 is dealing only with the ceremonies (“the comparison made by the Apostle refers to the form rather than to the substance.”) However, he arrives at some difficulty at v10 where he begins listing what Scripture says the New Covenant consists of – it consists of things that cannot be regarded as accidents but as the substance.
10 For this is the covenant that I will make, etc. There are two main parts in this covenant; the first regards the gratuitous remission of sins; and the other, the inward renovation of the heart; there is a third which depends on the second, and that is the illumination of the mind as to the knowledge of God. There are here many things most deserving of notice.
The first is, that God calls us to himself without effect as long as he speaks to us in no other way than by the voice of man. He indeed teaches us and commands what is right but he speaks to the deaf; for when we seem to hear anything, our ears are only struck by an empty sound; and the heart, full of depravity and perverseness, rejects every wholesome doctrine. In short, the word of God never penetrates into our hearts, for they are iron and stone until they are softened by him; nay, they have engraven on them a contrary law, for perverse passions rule within, which lead us to rebellion. In vain then does God proclaim his Law by the voice of man, unless he writes it by his Spirit on our hearts, that is, unless he forms and prepares us for obedience. It hence appears of what avail is freewill and the uprightness of nature before God regenerates us. We will indeed and choose freely; but our will is carried away by a sort of insane impulse to resist God. Thus it comes that the Law is ruinous and fatal to us as long as it remains written only on tables of stone, as Paul also teaches us. (2 Corinthians 3:3.) In short, we then only obediently embrace what God commands, when by his Spirit he changes and corrects the natural pravity of our hearts; otherwise he finds nothing in us but corrupt affections and a heart wholly given up to evil. The declaration indeed is clear, that a new covenant is made according to which God engraves his laws on our hearts, for otherwise it would be in vain and of no effect.
The second particular refers to the gratuitous pardon of sins. Though they have sinned, saith the Lord, yet I will pardon them. This part is also most necessary; for God never so forms us for obedience to his righteousness, but that many corrupt affections of the flesh still remain; nay, it is only in part that the viciousness of our nature is corrected; so that evil lusts break out now and then. And hence is that contest of which Paul complains, when the godly do not obey God as they ought, but in various ways offend. (Romans 7:13.) Whatever desire then there may be in us to live righteously, we are still guilty of eternal death before God, because our life is ever very far from the perfection which the Law requires. There would then be no stability in the covenant, except God gratuitously forgave our sins. But it is the peculiar privilege of the faithful who have once embraced the covenant offered to them in Christ, that they feel assured that God is propitious to them; nor is the sin to which they are liable, a hindrance to them, for they have the promise of pardon.
And it must be observed that this pardon is promised to them, not for one day only, but to the very end of life, so that they have a daily reconciliation with God. For this favor is extended to the whole of Christ’s kingdom, as Paul abundantly proves in the fifth chapter of his second Epistle to the Corinthians. And doubtless this is the only true asylum of our faith, to which if we flee not, constant despair must be our lot. For we are all of us guilty; nor can we be otherwise released then by fleeing to God’s mercy, which alone can pardon us.
And they shall be to me, etc. It is the fruit of the covenant, that God chooses us for his people, and assures us that he will be the guardian of our salvation. This is indeed the meaning of these words, And I will be to them a God; for he is not the God of the dead, nor does he take us under his protection, but that he may make us partakers of righteousness and of life, so that David justly exclaims, “Blessed are the people to whom the Lord is God (Psalm 144:15.) There is further no doubt but that this truth belongs also to us; for though the Israelites had the first place, and are the proper and legitimate heirs of the covenant, yet their prerogative does not hinder us from having also a title to it. In short, however far and wide the kingdom of Christ extends, this covenant of salvation is of the same extent.
But it may be asked, whether there was under the Law a sure and certain promise of salvation, whether the fathers had the gift of the Spirit, whether they enjoyed God’s paternal favor through the remission of sins? Yes, it is evident that they worshipped God with a sincere heart and a pure conscience, and that they walked in his commandments, and this could not have been the case except they had been inwardly taught by the Spirit; and it is also evident, that whenever they thought of their sins, they were raised up by the assurance of a gratuitous pardon. And yet the Apostle, by referring the prophecy of Jeremiah to the coming of Christ, seems to rob them of these blessings. To this I reply, that he does not expressly deny that God formerly wrote his Law on their hearts and pardoned their sins, but he makes a comparison between the less and the greater. As then the Father has put forth more fully the power of his Spirit under the kingdom of Christ, and has poured forth more abundantly his mercy on mankind, this exuberance renders insignificant the small portion of grace which he had been pleased to bestow on the fathers. We also see that the promises were then obscure and intricate, so that they shone only like the moon and stars in comparison with the clear light of the Gospel which shines brightly on us.
If it be objected and said, that the faith and obedience of Abraham so excelled, that hardly any such an example can at this day be found in the whole world; my answer is this, that the question here is not about persons, but that reference is made to the economical condition of the Church. Besides, whatever spiritual gifts the fathers obtained, they were accidental as it were to their age; for it was necessary for them to direct their eyes to Christ in order to become possessed of them. Hence it was not without reason that the Apostle, in comparing the Gospel with the Law, took away from the latter what is peculiar to the former. There is yet no reason why God should not have extended the grace of the new covenant to the fathers. This is the true solution of the question.
(Commentary on Hebrews 8:10)
Calvin’s argument in Hebrews 8 is that the only difference is accidental – in outward appearance, manner of revelation, emphasis, etc. Yet Scripture says the newness of the New Covenant is regeneration and forgiveness of sins. Calvin reasons that it only means that under the New Covenant “the Father has put forth more fully the power of his Spirit under the kingdom of Christ, and has poured forth more abundantly his mercy on mankind.” And yet, Abraham’s faith excelled ours and is the model of our faith. Calvin concludes that the real solution is to admit there is no reason to say God did not “extend the grace of the new covenant” to Abraham.
He was comfortable saying so because he had read Augustine, and that is precisely what Augustine taught.
10. The three last contrasts to which we have adverted (sec. 4, 7, 9), are between the Law and the Gospel, and hence in these the Law is designated by the name of the Old, and the Gospel by that of the New Testament. The first is of wider extent (sec. 1), comprehending under it the promises which were given even before the Law. When Augustine maintained that these were not to be included under the name of the Old Testament (August. ad Bonifac. lib. 3 c. 14), he took a most correct view, and meant nothing different from what we have now taught; for he had in view those passages of Jeremiah and Paul in which the Old Testament is distinguished from the word of grace and mercy. In the same passage, Augustine, with great shrewdness remarks, that from the beginning of the world the sons of promise, the divinely regenerated, who, through faith working by love, obeyed the commandments, belonged to the New Testament [Covenant]; entertaining the hope not of carnal, earthly, temporal, but spiritual, heavenly, and eternal blessings, believing especially in a Mediator, by whom they doubted not both that the Spirit was administered to them, enabling them to do good, and pardon imparted as often as they sinned. The thing which he thus intended to assert was, that all the saints mentioned in Scripture, from the beginning of the world, as having been specially selected by God, were equally with us partakers of the blessing of eternal salvation. The only difference between our division and that of Augustine is, that ours (in accordance with the words of our Saviour, “All the prophets and the law prophesied until John,” Mt. 11:13) distinguishes between the gospel light and that more obscure dispensation of the word which preceded it, while the other division simply distinguishes between the weakness of the Law and the strength of the Gospel. And here also, with regard to the holy fathers, it is to be observed, that though they lived under the Old Testament, they did not stop there, but always aspired to the New, and so entered into sure fellowship with it. Those who, contented with existing shadows, did not carry their thoughts to Christ, the Apostle charges with blindness and malediction. To say nothing of other matters, what greater blindness can be imagined, than to hope for the expiation of sin from the sacrifice of a beast, or to seek mental purification in external washing with water, or to attempt to appease God with cold ceremonies, as if he were greatly delighted with them? Such are the absurdities into which those fall who cling to legal observances, without respect to Christ.
Despite appealing to Augustine to demonstrate that all the saints from the beginning of the world belonged to the New Covenant, notice that Calvin acknowledges a difference between Augustine’s view and his own. He says his view makes the distinction between the Old and New Covenants a matter of obscurity and clarity, while Augustine makes it a matter of Law and Gospel. That is no small difference!
The reality is, Augustine did not agree with Calvin’s main point: that the Old and the New are the same covenant. He rejected it in very strong terms. Calvin found recourse in Augustine when he had to reconcile Scripture’s teaching regarding regeneration as a grace of the New Covenant, but that is because Augustine was much more biblical in his understanding of the differences between the Old and the New.
At all events, in those ancient Scriptures it is most distinctly written: “Behold, the days come, saith the Lord, that I will consummate a new testament with the house of Israel and with the house of Jacob; not according to the testament that I made with their fathers, in the day that I took them by the hand, to lead them out of the land of Egypt.” (Jer 31:31, 32) This was done on Mount Sinai. But then there had not yet risen the prophet Daniel to say: “The saints shall receive the kingdom of the Most High.” (Dan 7:18) For by these words he foretold the merit not of the Old, but of the New Testament. In the same manner did the same prophets foretell that Christ Himself would come, in whose blood the New Testament was consecrated. Of this Testament also the apostles became the ministers, as the most blessed Paul declares: “He hath made us able ministers of the New Testament; not in its letter, but in spirit: for the letter killeth, but the spirit giveth life.” (2 Cor 3:6) In that testament [covenant], however, which is properly called the Old, and was given on Mount Sinai, only earthly happiness is expressly promised. Accordingly that land, into which the nation, after being led through the wilderness, was conducted, is called the land of promise, wherein peace and royal power, and the gaining of victories over enemies, and an abundance of children and of fruits of the ground, and gifts of a similar kind are the promises of the Old Testament. And these, indeed, are figures of the spiritual blessings which appertain to the New Testament; but yet the man who lives under God’s law with those earthly blessings for his sanction, is precisely the heir of the Old Testament, for just such rewards are promised and given to him, according to the terms of the Old Testament, as are the objects of his desire according to the condition of the old man. But whatever blessings are there figuratively set forth as appertaining to the New Testament require the new man to give them effect. And no doubt the great apostle understood perfectly well what he was saying, when he described the two testaments as capable of the allegorical distinction of the bond-woman and the free,—attributing the children of the flesh to the Old, and to the New the children of the promise: “They,” says he, “which are the children of the flesh, are not the children of God; but the children of the promise are counted for the seed.” (Rom 9:8) The children of the flesh, then, belong to the earthly Jerusalem, which is in bondage with her children; whereas the children of the promise belong to the Jerusalem above, the free, the mother of us all, eternal in the heavens. (Gal 4:25, 26) Whence we can easily see who they are that appertain to the earthly, and who to the heavenly kingdom. But then the happy persons, who even in that early age were by the grace of God taught to understand the distinction now set forth, were thereby made the children of promise, and were accounted in the secret purpose of God as heirs of the New Testament; although they continued with perfect fitness to administer the Old Testament to the ancient people of God, because it was divinely appropriated to that people in God’s distribution of the times and seasons.
Augustine: Proto-1689 Federalist