Galatians 3:15-16

Brothers and sisters, let us think in human terms: Even an agreement made between two persons is firm. After that agreement is accepted by both people, no one can stop it or add anything to it. God made promises both to Abraham and to his descendant. God did not say, “and to your descendants.” That would mean many people. But God said, “and to your descendant.” That means only one person; that person is Christ.