A.T. Robertson Commentary Acts 7:8

"And he gave him the covenant of circumcision: and so [Abraham] begat Isaac, and circumcised him the eighth day; and Isaac [begat] Jacob, and Jacob the twelve patriarchs." — Acts 7:8 (ASV)

The covenant of circumcision (διαθηκην περιτομης). A covenant marked by (genitive) circumcision (no article) of which circumcision is the sign (Romans 4:11) as set forth in Ge 17:9-14. In the ancient Greek διαθηκη was usually will (Latin, testamentum) and συνθηκη was used for covenant (συν, together, rather than δια, between). But the LXX and the N.T. use διαθηκη for covenant (will in Heb 9:15f.) as Lightfoot on Ga 3:16 says: "The LXX translation and New Testament writers probably preferred διαθηκη as better expressing the

free grace of God than συνθηκη."

And so (κα ουτως). After the covenant was made and as a sign and seal of it.