The Mosaic Covenant - Is the Law Against the Promises of God?

In ecuse thres, Paul says that we are not justified by law. We are justified through faith in christ and the promise he gives us. He then goes on to define it a little further: for you are all sons of god who have been baptized into Christ. What does this mean? It's an expliiation of the repudiation of law which paul is talking about here. In fact, when somebody asks if they can be justified by law,  we are clearly talking about something else.