For background, see my post Contradiction in the Westminster Confession
I stumbled upon some very succinct notes from Kline articulating the view Karlberg ascribes to Kline in that post. Comments on the A. A. Hodge One-Covenant Construction of the Redemptive Order consists of brief comments from Kline arguing against the view of the Covenant of Grace articulated in the WCF/WLC. In summary, he notes:
Through its failure to distinguish satisfactorily the two very different arrangements in the redemptive order [CoG and CoR] and the resultant blurring together of contradictory elements, the one-covenant construction of A. A. Hodge (and WCF/WLC) has at least these liabilities:
1. It leads to a definition of the covenant community (church) in Baptistic terms as consisting of believers or the elect, contrary to the Presbyterian doctrine that the church consists of those who profess Christian faith and their children.
2. Arguably (as I suggested at the faculty forum), it has contributed by its formal fusing of the works and grace principles to the confusion of the two and even the repudiation of the works principle in the teachings of Fuller, Shepherd, et. al.
These are precisely the two points of contention with WCF I have striven to work out and articulate on this blog.