S. M. Baugh, “Galatians 3:20 and the Covenant of Redemption,” Westminster Theological Journal 66, no. 1 (2004): 49-70.
Baugh’s own summary:
The interpretation of Gal 3:20 offered here flows particularly out of an analysis of v. 15 running through v. 22. I view v. 15 as Paul invoking an analogy from testamentary practices of the day, which prohibited any party who was not the testator from emending or annulling a last will and testament. This would have been understood across the broad spectrum of ancient legal situations in antiquity—as indeed it is so understood today—without any special legal training or involving a legal practice restricted to some particular region.
What makes understanding v. 15 correctly so important is that it clarifies the purpose of Paul’s analogy. It shows us that the law, represented by Moses its mediator, is incompatible with the promissory Abrahamic covenant when put to the wrong use. In v. 17, Paul applies this analogy to this effect by saying the law could not annul the inheritance by changing the principial basis of inheritance from a gracious grant “from faith” to a basis of personal law-keeping. The new covenant represents direct continuity with the Abrahamic covenant on this score, and Paul emphasizes this point by declaring us heirs alongside Abraham repeatedly in this chapter (vv. 6–9, 14, and 29). In covenant theology, this continuity and development is expressed when we confess that Christ represents the substance of the one covenant of grace inaugurated immediately after the fall and yet administered in different ways in the course of redemptive history.
However, Paul moves briefly but most profoundly behind the historical development of the covenant of grace into the eternal realm in vv. 19–20. What started him in this direction was when he mentioned that the terminus ad quem of the Mosaic administration of law—which served in part as a “ministry of condemnation” for transgressions (v. 19; 2 Cor 3:9)—was the arrival of the Seed to whom the promises given to Abraham were ultimately oriented. The clear assumption here is that the Seed existed before he came, for the promises were spoken to him when Abraham heard them. This, incidentally, is why Paul has to comment that the Son of God was “born of a woman” when he did finally come in the fullness of time (Gal 4:4), for the Son did not come in his divine glory, but in servile guise as a true man (Phil 2:6–8). This was not a “hyiophany” but a genuine incarnation.
So then, once Paul has reflected on the Son’s pre-incarnate existence in Gal 3:19, it was quite natural for him to clinch his argument about the impossibility of changing the basis of inheritance from grace, faith, and promise to that of personal obligation and law-keeping by invoking the intratrinitarian life of God as the foundation of the covenant with Abraham. He was already dwelling on the eternal existence of the Son as Seed-to-come.
When Paul does clinch his argument, he does so in the most profound way, a way which has puzzled interpreters who were unable or unwilling to follow Paul into the heavens. The mediation of the law through angels by the hand of Moses was not an “eternal ordinance ordained and written in the heavenly tablets” and thereby representing an intractable principle of inheritance of God’s promises overthrowing faith in Christ. Rather, the promises of God to a fallen world are rooted in his sovereign, intratrinitarian counsel, traditionally called the pactum salutis, which Moses did not and could not mediate, for God is one (69-70).
There is much I learned from this article, and much I agree with. I’m tempted to agree with Baugh’s interpretation of vv. 19-20, as it would be an elegant interpretation of those difficult verses to say that the point is that no mediator is necessary for the promise because the promise is made within the one Godhead. What prevents me from embracing Baugh’s position on those verses, however, is that Paul in this passage is clearly connecting the promises with the Abrahamic covenant rather than to the covenant of redemption. Though I think the covenant of redemption is a legitimate theological category, I have difficulty seeing a clear indication that Paul is making use of it here.