An angel announced the births of Isaac, Samson, John, and Jesus

[tonychanyt]

There were four cases where an angel showed up to announce to a childless person a future son was to be born.

An angel told Abraham in Genesis 18:

10b “I will surely return to you about this time next year, and Sarah your wife will have a son.” Now Sarah was listening at the entrance to the tent, which was behind him.

An angel told Manoah's wife in Judges 13:

3b “It is true that you are barren and have no children; but you will conceive and give birth to a son. 4Now please be careful not to drink wine or strong drink, and not to eat anything unclean. 5For behold, you will conceive and give birth to a son. And no razor shall come over his head, because the boy will be a Nazirite to God from the womb.

The angel Gabriel told Zechariah in Luke 1:

13b “Do not be afraid, Zechariah, for your prayer has been heard, and your wife Elizabeth will bear you a son, and you shall call his name John. 14And you will have joy and gladness, and many will rejoice at his birth, 15for he will be great before the Lord. And he must not drink wine or strong drink, and he will be filled with the Holy Spirit, even from his mother’s womb."

Both Samson and John the Baptizer were Nazirites.

Gabriel told Mary:

30b “Do not be afraid, Mary, for you have found favor with God. 31And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus."

Both Isaac and Jesus were willing participants in their respective sacrifices.