The faith of Abraham concerns justification.The Law of Moses concerns transgression. Law has never been the basis for justification. The model for New Testament justification is rooted in the Abrahamic model and not the Mosaic model. That was the whole point of “Paul’s Gospel to the Galatians.”
-JDC-
The law came to protect the relationship type that Abraham had with God. A walk of faith that brought justification was in danger of being list because of the transgression of mankind. Therefore, God sent the Law, our Schoolmaster, until Christ would come and fulfill the Law and thus perfect the relationship between man and God of faith and justification.
-RW-