[3:15] My friends, I am going to use an everyday example: when two people agree on a matter and sign an agreement, no one can break it or add anything to it.
[3:16] Now, God made his promises to Abraham and to his descendant. The scripture does not use the plural “descendants,” meaning many people, but the singular “descendant,” meaning one person only, namely, Christ.
[3:17] What I mean is that God made a covenant with Abraham and promised to keep it. The Law, which was given four hundred and thirty years later, cannot break that covenant and cancel God's promise.
[3:18] For if God's gift depends on the Law, then it no longer depends on his promise. However, it was because of his promise that God gave that gift to Abraham.
[3:19] What, then, was the purpose of the Law? It was added in order to show what wrongdoing is, and it was meant to last until the coming of Abraham's descendant, to whom the promise was made. The Law was handed down by angels, with a man acting as a go-between.
[3:20] But a go-between is not needed when only one person is involved; and God is one.