Genesis 17:5
Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations have I made thee. Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations have I made thee.
After nearly twenty-five years in Canaan God appeared as the Almighty God and commanded a life of blameless devotion before Him, and Abraham fell facedown in awe. Then Abram was renamed Abraham, which means father of a great multitude, as a token that the promise to make him a father of many nations would be fulfilled. The renaming belongs to God's covenant with Abraham in which He promised to multiply him, to establish an everlasting covenant with him and his descendants, and to be their God. The sign of that covenant, circumcision, marked Abraham and his descendants as set apart from other nations and pledged them to keep the covenant by living separately and obeying God.
The covenant promise to make Abraham the father of many descendant nations was cherished by Isaac and Rebekah as their great hope and taught to Esau and Jacob as the birthright. That birthright meant more than material wealth, conferring spiritual preeminence as priest of the family and continuance of the family line from which the Redeemer of the world would come. It also obligated its holder to devote his life to God's service and obey God's requirements as Abraham had done, seeking God's will in marriage, family relations, and public life, since God's law was the condition of the covenant. Isaac made those privileges and conditions known to his sons and declared Esau entitled as the eldest, but Esau had no love for devotion and viewed the law and spiritual requirement as a hateful bondage, desiring only freedom for self-indulgence, power, riches, and wild living, while Rebekah discerned that the promised heritage was intended for Jacob.