And God gave Abraham a covenant [a formal agreement to be strictly observed] of [which] circumcision [was the sign]; and so [under these circumstances] Abraham became the father of Isaac, and circumcised him on the eighth day; and Isaac [became the father] of Jacob, and Jacob [became the father] of the twelve patriarchs.

For it is written that Abraham had two sons, one by the slave woman [Hagar] and one by the free woman [Sarah].

By faith even Sarah herself received the ability to conceive [a child], even [when she was long] past the normal age for it, because she considered Him who had given her the promise to be reliable and true [to His word].

At the set

But God said, “No, Sarah your wife shall bear you a son indeed, and you shall name him Isaac (laughter); and I will establish My covenant with him for an everlasting covenant and with his descendants after him.

He said, “I will surely return to you at this time next year; and behold, Sarah your wife will have a son.” And Sarah was listening at the tent door, which was behind him.

For this is what the promise said: “About this time [next year] I will come, and Sarah shall have a son.”

General references

Now the time had come for Elizabeth to give birth, and she gave birth to a son.

And so, having patiently waited, he realized the promise [in the miraculous birth of Isaac, as a pledge of what was to come from God].