My parents set up irrevocable trust agreements for each of us seven children. Once the trust papers had been signed, they could not be annulled or changed. These irrevocable trusts demonstrate our parents' generous, unconditional love for us.
In Galatians 3:15-18 Paul uses a similar legal document to illustrate the nature of the Abrahamic covenant: Brothers, let me take an example from everyday life. Just as no one can set aside or add to a human covenant that has been duly established, so it is in this case (v. 15). This "irrevocable trust agreement" that God made with Abraham is described in terms of the beneficiary of the trust (v. 16), the date of the trust (v. 17) and the condition for inheritance (v. 18). Our study of these terms of the Abrahamic covenant will enable us to appreciate the gracious, unconditional nature of God's love for us.