“This is what the promise said.
‘About this time,
I will return.
Sarah shall have a son.’”
ἐπαγγελίας γὰρ ὁ λόγος οὗτος Κατὰ τὸν καιρὸν τοῦτον ἐλεύσομαι καὶ ἔσται τῇ Σάρρᾳ υἱός.
Paul said that this is what the promise said (ἐπαγγελίας γὰρ ὁ λόγος οὗτος). “About this time (Κατὰ τὸν καιρὸν τοῦτον), I will return (ἐλεύσομαι). Sarah shall have a son (καὶ ἔσται τῇ Σάρρᾳ υἱός).” Paul talked about the Israelite promise from Yahweh, through the three visitors to Sarah and Abraham that she would have a son, Isaac. Obviously, this story would have been difficult for the gentiles, but familiar to the Jewish Christians. Paul used his knowledge of Genesis, chapter 18:10-14, where the three visitors asked Abraham where Sarah was. Then, one of the visitors said that he would return next season and Sarah would have a son. Paul omitted the fact that Sarah laughed at him. Sarah did not have any children at this time, so she did not expect to have a son, but a year later she did have Isaac. Paul used the example of Sarah to prove his point about promises. Do you keep your promises like God did to Sarah?