Where did the revelation of salvation by faith and grace come from?
The revelation of salvation by faith and grace came from the risen Christ, who revealed this new concept to the Apostle Paul. It was not derived from the Law, which was done away in Christ, but was God's gracious provision because Christ finished redemption through His death, burial, and resurrection.
Les teaches that the Law was given to Israel to prepare them for the coming Messiah, but in their unbelief they failed it from start to finish. When Christ finished the work of redemption through His death, burial, and resurrection, the whole system of Law was done away and abolished, because something far better had come. Christ then revealed to the Apostle Paul this whole new concept of salvation by faith because of God's grace, and nothing added. The average Jew in blindness still ties himself to the Law, and the veil remains when Moses is read, so they cannot see that the Law has come to an end and something better has come in its place.