When Paul uses "law", he means the Old Covenant.
Gal 3:17 And this I say, that the covenant, that was confirmed before of God in Messiah, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect.
The Old Covenant was added to the Abrahamic Covenant to deal with sin / transgressions of the law.
Rom 5:20 Moreover the law entered, that the offence (transgressions) might abound. But where sin abounded, grace did much more abound:
Yahweh wanted people to know beyond a shadow of a doubt how sinful they were so that when Messiah came, they would see their need for him. The Old Covenant provided a temporary way to deal with those transgressions.
So, when Paul says, "till the seed should come", he is saying the "covenant" that was added would cease. That is why he goes into his teaching about the two covenants in the next chapter. He is showing us why that Old Covenant needed to end. However, the law did not end. It would be written on hearts and minds under the NC.
"Thus the heavens and the earth were finished, and all the host of them. And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made."
It is illogical to assume that Yahweh made Adam on day 6, then set apart and blessed the 7th day, but failed to tell Adam that the 7th day was set apart as holy time with a blessing upon it.
Yeshua said, "The Sabbath was made for man ...". He did not say, "The Sabbath was made for Jews" or "The Sabbath was made only for men who lived after Sinai, but until my death." The Sabbath was made for every man that will ever live. It is Yahweh's gift to mankind and the means by which we remember His Creation and who it is that sanctifies us (Ex 20:11; 31:13).