Throughout the Old Testament, there was a progression of covenants with the Fathers of our Faith, leading up to our final covenant with Jesus.  Even though we don't think in terms of covenants much today in the Old Testament, a covenant, specifically a blood covenant, was the most powerful and binding agreement known to man. It was a permanent joining of two people, two families, or two groups of people. This is exactly how much God wants to be in covenant with us.