When God visited Abraham by the oaks of Mamre, He said that he would return in one year when Sarah had a son. Did you ever think of this as a physical manifestation of God like the year prior?
The text doesn’t record a meal or dialogue between God and Abraham or Sarah on this second visit. But Genesis 21:1 says that God visited Sarah as He said. A year ago, God was standing physically before Abraham when He said that He would return. How would Abraham take that other than to think God would stand before them again when Sarah had a child. Should we understand that verse any other way? Interestingly, nothing more is said about the visit other than it happened. We’ll just have to leave it at that.
So, Isaac was born at the time when God said. And Abraham circumcised Isaac on the eighth day as the Lord commanded.
On the day that Isaac was weaned, Abraham had a great feast. And that’s all that is said about the birth of Isaac. It’s kind of like a small filler article in a newspaper. There wasn’t a feast when Isaac was born, just at the time of his weaning. Isaac came quietly on the scene after all the anticipation of the promise of his coming. Does that remind you of anything?
The Messiah came quietly on the scene in the small town of Bethlehem. The promise was well known. They were waiting, but they missed it. Only a small group of shepherds heard the news.