Rashi on Genesis 17:9/רש"י על בראשית י״ז:ט׳

1ואתה AND AS FOR THEE — This ו (of ואתה) connects this verse with the preceding matter (v. Gensis 17:4, thus setting ואתה of here in contrast with the ואני of there): “As for Me, behold My covenant is with thee” — “and as for thee, thou shalt be careful to keep it”. And what constitutes the “keeping” of it? THIS IS MY COVENANT WHICH YE SHALL KEEP… EVERY MALE AMONGST YOU [SHALL BE CIRCUMCISED].