The Jews who descended from Abraham were never really the nation we associate with greatness. They did not conquer and build a great empire like the Romans did or build large monuments like the Egyptians did with the pyramids. Their fame comes from the Law and Book which they wrote; from some remarkable individuals that were Jewish; and that they have survived as a somewhat different people group for thousands of years. Their greatness is not because of anything they did, but rather what was done to and through them. The promise says repeatedly “I will …” – that would be the power behind the promise. Their unique greatness happened because God made it happen rather than some ability, conquest or power of their own.
The promise to Abraham came true because he trusted a promise and chose to live differently than others. Think how likely it was for this promise to have failed, but instead it has happened, and is continuing to unfold, as it was stated thousands of years ago. The case is strong that the promise came true only because of the power and authority of the Promise-Maker