The fountainhead of the Abrahamic covenant and its blessings flow from Christ Jesus. One of the blessings secured by the Abrahamic covenant is the promised indwelling of the Holy Spirit, which was prefigured by circumcision of the flesh and pointed to the circumcision of the heart by the Spirit. (Rom 2:29, Col 2:11) The Spirit is the ratification of the Abrahamic Covenant upon the hearts of those who are in Christ … Abraham’s true children.
Gal 3:14-16 so that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we might receive the promised Spirit through faith. 15 To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified. 16 Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ.
The Abrahamic Covenant and its promises were made to Abraham AND to Jesus Christ (the Offspring). Since the promises were made to Messiah, then the substance of them are purely eschatological, spiritual, and redemptive in nature, not fleshly, earthy, nationalistic, or geopolitical.
Gal 3:17-19 This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void. 18 For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise. 19 Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary.
The law was added until the promised offspring should come. The “offspring” is Jesus Christ. He came as “the promise” fulfillment to the true children of Abraham, both believing Jews and Gentiles. Jesus IS the very substance and promise of the Abrahamic Covenant who comes to his people. The covenant that God made with Abraham was Jesus. Jesus is the Abrahamic Covenant Incarnate. All of the covenant promises of the Old Covenant age (Adamic, Abrahamic, Davidic, etc.) find their convergent fulfillment in the Word Incarnate, in one united New Covenant.
Jesus even indicates that he is the fulfillment of the Abrahamic covenant, when speaking of Abraham’s faith in the covenant promises. Through the promises Abraham saw Christ’s day and was glad. (John 8:56)
The Abrahamic geographical land promise is now understood by Paul to be the entire world. (Rom 4:13) This present world has been redeemed by Christ and is “eagerly longing for the revealing of the sons of God”, at which time “the creation itself will be set free from its bondage to corruption and obtain the freedom of the glory of the children of God.” (Rom 8:19-21) The present Jerusalem is in bondage and we are awaiting for the appearing of the heavenly Jerusalem, of which we are now members. (Gal 4:25-26)
Though Abraham received promises of a physical land, son, nation, kingdom, etc, he forsook the earthly nature of them, calling himself a stranger and exile in the earth, and saw “by faith” that these promises were eschatological (heavenly) realities to be fulfilled in Christ. (Heb 11:8-16)
Gal 3:20-21 Now an intermediary implies more than one, but God is one. 21 Is the law then contrary to the promises of God? Certainly not! For if a law had been given that could give life, then righteousness would indeed be by the law.
Paul is saying that it is the Promise (Christ Himself) that gives life and righteousness, not the law.
Gal 3:22-23 But the Scripture imprisoned everything under sin, so that the promise by faith in Jesus Christ might be given to those who believe. 23 Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed.
Before faith (Christ) came the Old Covenant people were imprisoned under sin and held captive under the guardianship of the law.
Gal 3:24 So then, the law was our guardian until Christ came, in order that we might be justified by faith.
Men can never be justified OR sanctified by the law . . . but only through faith in Christ alone. The faith which justifies is the same faith which also sanctifies.
Gal 3:25-27 But now that faith has come, we are no longer under a guardian, 26 for in Christ Jesus you are all sons of God, through faith. 27 For as many of you as were baptized into Christ have put on Christ.
Believers are no longer imprisoned “under sin” and held captive “under the law” but are now sons of God and clothed with Christ, our righteousness and life!
Gal 3:28-29 There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus. 29 And if you are Christ’s, then you are Abraham’s offspring, heirs according to promise.
Christ is Abraham’s Offspring (singular). Those who are covenantally united to this Offspring through faith, being “in Christ”, are joined to his singular covenant Body and become partakers of the blessings promised to him.