‘And Abraham was old and well stricken in age, and Yahweh had blessed Abraham in all things.'
This is a brief summary of Abraham's life which is now coming to its end. It deliberately emphasises that the future is now with Isaac. The blessings were now to begin on him.
We would not gather from this that after the death of Sarah Abraham would remarry, would beget six sons, and would see them live to sufficient maturity to be sent away to live lives independently of the tribe (chapter 25). But that is only incidental to the main record and the maintaining of the covenant line. Before that is introduced the covenant succession must be made clear.