According to many of the Jews living at the time, obedience to Mosaic law was the means by which one earned God’s favour and the right of inheritance (life in God’s presence). Having demonstrated that this is not the case, Paul now needs to explain why the law was given to God’s people.
19 Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary.