All who run to Christ are saved by his grace and profit from his gift. But those who wish to find justification from the Law will also fall from grace. They will not be able to enjoy the King’s loving-kindness because they are striving to gain salvation by their own efforts; they will draw down on themselves the curse of the Law because by the works of the Law no flesh will find justification.

What does this mean? That he has justified our race not by right actions, not by toils, not by barter and exchange, but by grace alone. Paul, too, made this clear when he said: “But now the justice of God has been made manifest apart from the Law.” But the justice of God comes through faith in Jesus Christ and not through any labor and suffering.” 

-St John Chrysostom on Justification, (347 – 407 AD) Discourses Against Judaizing Christians. Discourse 1:6-II:l