Why does a baby boy receive his name at his brit mila?

G-d gave Abraham his full name (i.e., changing his name from Abram to Abraham) when He said, "As for Me, behold, My covenant is with you." Thus we see that a name is given at the time when a covenant - in Hebrew, bris - is made. Also, the Torah tells us that Abraham named his son Isaac and then immediately afterward it relates: "And Abraham circumcised his son..."