Moses gave you the teaching about circumcision (although it didn’t come from Moses but from our ancestors). So you circumcise a male on a day of rest—a holy day.
“God gave Abraham circumcision to confirm his promise. So when Abraham’s son Isaac was born, Abraham circumcised him on the eighth day. Isaac did the same to his son Jacob, and Jacob did the same to his twelve sons (the ancestors of our tribes).
This is what I mean: The laws ⌞given to Moses⌟ 430 years after God had already put his promise ⌞to Abraham⌟ into effect didn’t cancel the promise ⌞to Abraham⌟.