Even Under Law, God Remembered His Covenant — with Abraham

"Moreover the law entered, that the offence might abound. But where sin abounded,
grace did much more abound:" (Romans 5: 20)

The Ten Commandments was never God's main agenda. The blessings of God on man, the Blessing to Abraham and all his seed, with Jesus as the first-born of many brethren, was God's main agenda, a life of rest and ease in which every human being would believe on Jesus for everything, since by His death and resurrection we receive all things (Romans 8: 31-32)

"The law entered". . .A better translation would read "The law came in through the side" or "the law entered by the way. . " as a parenthetical, not the main stay.

For this reason, Paul would write to the Galatians:

"23But before
faith came, we were kept under the law, shut up unto the faith which should
afterwards be revealed. 24Wherefore the
law was our schoolmaster to bring us unto Christ, that we might be
justified by faith. 25But after that
faith is come, we are no longer under a schoolmaster." (Galatians 3: 23-25)

In the next chapter, Paul refers to the tension in Abraham's household, between his bondmaid Hagar and his lawful, gracious wife Sarah, and through this allegory he vehemently emphasizes the end of the Old Covenant of Law to be replaced by the New Covenant of Grace:

"Now we, brethren, as Isaac was, are the children of promise. 29But as then he
that was born after the flesh persecuted him that was born after the
Spirit, even so it is now.