Hebrews 6:14

‘Saying, “Surely blessing I will bless you, and multiplying I will multiply you.’

And that promise was that He would certainly bless him, and would certainly multiply him, so that throughout the whole world God’s own chosen ones would be brought into being, those who would become sons of Abraham, who would walk as Abraham walked, and would be blessed through him (so that if necessary He would and could turn stones into sons of Abraham - Matthew 3:9). His purpose was set and fixed and nothing could stop it. Thus those who enter into the blessing of Abraham through becoming God’s children by faith (Romans 4:12-13; Romans 4:24; Galatians 3:7-9; Galatians 3:14; Galatians 3:29), have the assurance that they have come within the unchangeable promise of God, a promise which will never fail. When God made His oath to Abraham He made it to all who are His own.