Was the Law a covenant, like the Abrahamic and Davidic covenants?
Yes. The Law was a covenant, just like the Abrahamic covenant and the Davidic covenant. It was an agreement God made, which He could never change or withdraw, and it settled forever because God made it. It came 430 years after the promise to Abraham, when Israel received the Law at Sinai.
Les teaches that Paul is speaking of the covenant in verse 17 as confirmed before of God in the person of Christ, and he identifies that covenant as the Law. The Law was a covenant, just as the Abrahamic and Davidic covenants were covenants. It was an agreement God made that He could never change or withdraw, and it settled forever because God made it. Les places it 430 years after the promise to Abraham that the seed would come from him, when Israel came out of Egypt and received the Law at Sinai. He also notes that Scripture's mention of 430, 400, and 490 years is not a contradiction.