By faith Abraham, even though he was past age—and Sarah herself was barren—was enabled to become a father because he considered him faithful who had made the promise. And so from this one man, and he as good as dead, came descendants as numerous as the stars in the sky and as countless as the sand on the seashore. (Heb. 11:11-12)The first verse has to do with God’s promise to Abraham, which was fulfilled when he was 100 years old, because Abraham knew that God was faithful and would keep his promise. God kept his promise!
They will say, "Where is this 'coming' he promised? Ever since our fathers died, everything goes on as it has since the beginning of creation"…The Lord is not slow in keeping his promise, as some understand slowness. He is patient with you, not wanting anyone to perish, but everyone to come to repentance. (2 Pet. 3:4, 9)
The second passage has to do with the promise of Jesus to return to Earth. He gives us the reason for the seeming delay. He kept this promise to Abraham, and He will keep His promise to us.