Chapter 21, verse 5: "And Abraham was an hundred years old, when his son Isaac was born unto him."
This means that Sarah was ninety years old. Can you imagine having a baby at that age? What an amazing miracle!
Even though God had told Abraham that Isaac would be his heir, Abraham trusted God when He told him to sacrifice his son. Do we have that kind of faith and trust in God? I hope so, but some days, I wonder.
The next chapters are Matthew 25-28.