|Moses, Reading the Law|
Why did it matter among what nation the Redeemer would be born? That goes back to the original promise of the Gospel, Genesis 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 promise was given immediately after the Fall, and especially touched Eve, the first human to give in to the temptations of Satan. It was a balm to her conscience to know that her descendant would also be the means of undoing what she and Adam had done. That is why the lineage of Christ is so carefully recorded. Of course, all mankind is the seed of Eve in a general sense, but His lineage is laid out explicitly, legally (i. e., covenantally) in Matthew 1, and genetically in Luke 3. A record is given of exactly in what way He represented her lineage. In our culture, that isn't considered important, but in theirs it was.
What makes me especially to marvel is that this story is carried all the way to the other end of the Bible. In Revelation 12:1-6, the Apostle John describes a woman who gives birth to a son, and a red dragon who persecutes both her and that son. I believe that the woman represents both Eve personally and the covenant people of Israel federally, and the son is, of course, Jesus Christ (see also Rom. 16:20). John explicitly tells us that the dragon is the serpent from the garden (Rev. 12:9). This is the end of the need for the restriction of the lineage, which is why God does away with the ceremonial law, and opens the Church to the Gentiles, those who had formerly been legally unclean (both aspects are described in the account of Peter's dream in Acts 10:10-29; see also Eph. 2:11-16).
This is why I insist that the Mosaic covenant is not a covenant of works, but is rather a temporary administrative stage of the covenant of grace. It was a necessary preparation for the coming of the full salvation that we have in Jesus Christ. It is not, and never was, an opportunity for the Jews - or anyone else - to earn their way to eternal life through good works. This is clear even in its establishment. The account of the giving of the Ten Commandments is found in Exodus 20:1-17. However, verse 2, the Preamble, says, "I am the Lord your God, who brought you out of the land of Egypt, out of the house of slavery." Before giving the shalls and shall-nots, God reminds the people of the redemption that He has already provided them, as the foundation on which the Law was to be built. Justification came before the Law (Rom. 4:10, 14; Gal. 3:17).
Contrary to the teachings of classical dispensationalism, there was never a time - i. e., after the Fall of Adam - in which any man could be saved by works. In Adam, we all became sinners (Rom. 5:12). We start life as sinners (Psalm 51:5, 58:3). This is the key: sin does not make us sinners; we sin because we are already sinners. It is comparable to a runner in a race who runs facing the wrong way; no matter how fast he runs, he is incapable of winning the race. If that weren't the case, then Jesus would never have needed to come, to suffer, and to die on the cross. As Paul says (Gal. 3:21-22), "if a law had been given that could give life, then righteousness would indeed be by the law. But the Scripture imprisoned everything under sin, so that the promise by faith in Jesus Christ might be given to those who believe."