Yahweh paid attention to Sarah
Here the phrase "paid attention to" refers to Yahweh helping Sarah have a baby. AT: "Yahweh helped Sarah" (See: rc://en/ta/man/translate/figs-explicit)
bore a son to Abraham
"gave birth to Abraham's son"
in his old age
"when Abraham was very old"
at the set time of which God had spoken to him
"at the exact time that God had told him it would happen"
Abraham named his son, the one who had been born to him, whom Sarah bore to him, Isaac
"Abraham named his newborn son, the one Sarah gave birth to, Isaac" or "Abraham named their newborn son Isaac"
Abraham circumcised his son Isaac when he was eight days old
"When his son Isaac was eight days old, Abraham circumcised him"
"8 days" (See: rc://en/ta/man/translate/translate-numbers)
had commanded him
"had commanded Abraham to do"