Galatians 3:19-20

19So we could ask: Why did God give his Law to his people after his promise to Abraham? He gave his Law to show them which things are wrong. It would have authority until Abraham's special descendant would come. That was the descendant that God had promised to bless. God used angels to give his Law to his people. It was Moses who received the Law from God, and Moses then took it to God's people.

20But God himself gave his promise to Abraham. It was not necessary to have somebody in between, like Moses.