John Gill Commentary Genesis 17:9

"And God said unto Abraham, And as for thee, thou shalt keep my covenant, thou, and thy seed after thee throughout their generations." — Genesis 17:9 (ASV)

And God said to Abraham, you shall keep my covenant
therefore
Observe the sign or token of it, circumcision, in the manner after related:

you, and your seed after you, in their generations ;
in successive ages until the Messiah come, the end of the law for righteousness.