Any discussion of the covenant of works and substitutionary atonement assumes the biblical principle of corporate solidarity. According to this concept, a group of people is so identified with one person that what is said of the individual can also be said of the group. Romans 5:12–21 illustrates this idea. Adam was chosen to represent his descendants; so, when he fell, all people fell. Jesus, as the second Adam, represents His people; thus, His perfect obedience to God enables those of us who trust Christ to be counted as having also kept the Law.
Paul has corporate solidarity in view in Galatians 3 when He uses “offspring” both for one person (Christ, v. 16) and for many (believers, v. 29). The apostle’s identification of Jesus as Abraham’s offspring to whom life, land, and blessing was promised (Gen. 12:1–3; 15; 17) refers to the people of God, the oneness of the seed accentuating their unity. Christ as Abraham’s one offspring to whom God made His promises is a concise way to say redemption was pledged to the one family unified in the Messiah, who is the truest expression of this people.
This helps us understand Galatians 3:19–20. In prioritizing the Abrahamic covenant above Moses, Paul realizes his readers will question the Law’s purpose. If Abraham’s covenant is primary, why did Yahweh give the Mosaic law at all (Gal. 3:19a)? Paul answers that the Law was given to serve the promise, an idea we will explore in the days ahead. Our interest today is in Paul’s cryptic statements about the Law being ordained through a mediator and the singularity of God (v. 20): “Now an intermediary implies more than one, but God is one.”
The Bible suggests that God revealed the Mosaic law through angels as intermediaries (Deut. 33:2), indicating the presence of multiple agents in the act. This same Law split mankind into many families (Jews, many different tribes of Gentiles). Since God is one, He has always sought to bless one family of Abraham, and so the Law that divides could not have been a permanent design. Returning to the Law reintroduces the temporary divisions put in place under Moses, violating God’s intent to have all nations included in Abraham’s one family, a unity that reflects the oneness of our Creator Himself.