- Gen. 3:15 with Eph. 2:12; Gal. 4:4; Heb. 11:13; Luke 2:25, 38; 23:51; Rom. 4:13-16; Gal. 3:15-22; Rev. 13:8[2]
The covenant of works that was given to Adam was broken by sin and thereby made unprofitable unto life (see also chapter 6:1). Now, it only administers its curse—death. Therefore, God was pleased to give forth the promise of Christ (Gen. 3:15; Eph. 2:12) as He had purposed to save the elect by Christ from all eternity. In this promise of Christ, the gospel was revealed as the means of calling the elect (Gal. 3:8; Luke 2:25, 38). As the gospel was revealed in this promise, God worked to beget in the elect faith and repentance so that they would embrace this promise, which was effectual for the conversion and salvation of sinners (Gal. 3:15-22). This promise of Christ was, essentially or in substance, the promise of the gospel and salvation, which is what Christ accomplished on behalf of the elect.
Salvation was always through Christ, whether people were consciously aware of that or not. They were saved by faith alone and by not works. By loosely reading the Old Testament and seeing the absence of the cross, we may think that salvation was by works under the Old Testament, but now, in the New Testament era, it is by grace. This is completely false and a grave mistake. Salvation has always been by grace. The reason that this is so is because the Adamic Covenant (see here), which could have provided eternal life if Adam obeyed, was broken. When that covenant was broken, the promise of eternal life by obedience was likewise broken and became unprofitable for Adam’s fallen and sin-cursed descendants. The Covenant of Works which was made with Adam in Eden lost the ability to give eternal life because it is now broken. That covenant did not contain provisions for atonement and now it could only administer the curse of that covenant—death. We see in Genesis 3 that just after God, the covenant Lord, confronts Adam and Eve with their sin, He likewise gives the promise of the Savior:
Gen. 3:15 I will put enmity between you and the woman, and between your offspring and her offspring; he shall bruise your head, and you shall bruise his heel.”
This is indisputably a promise of the Savior, the first one and that is why it is called the Proto-Evangelium, meaning, the first (giving-out of the) gospel. God promises a Seed, an Offspring Who would conquer the serpent, who is the Devil. At this point of time, it seems pretty vague, but as time goes by we come to know more about this Offspring and Seed. For example, Abraham is promised that in his “offspring shall all the nations of the earth be blessed” (Gen. 22:18). So now we know not only He will be the child of Eve, but will also be a descendent of Abraham. From Genesis 49:10 we learn that the Offspring and the Messiah will come from the loins of Judah. As we progress in biblical revelation, we come to learn more about the identity of the Messiah. Later it will be revealed that He will be a son of David (2Sam. 7) and so forth. It is not that the original Covenant of Works made with Adam has been completely done away with, but that it can no longer give life. The only thing it administers is its curse—death—under which all outside of Christ lie. Death is the wage of sin (Rom. 3:23...