Arcana Coelestia #2637
2637. 'When Isaac his son was born to him' means when the Lord's Rational was made Divine. This is clear from the meaning of 'being born' as being manifested, dealt with in 2584, 2621, 2629, and from the representation of 'Isaac' as the Divine Rational, dealt with in 2630. The latter is said 'to be born' to Abraham when it has been made Divine, as also in verse 3 above, 'Abraham called the name of his son born to him', see 2628.
Isaiah 66:7-9
7
"Before she travailed, she brought forth; before her pain came, she delivered a son.
8
Who has heard such a thing? who has seen such things? Shall a land be born in one day? shall a nation be brought forth at once? for as soon as Zion travailed, she brought forth her children.
9
Shall I bring to the birth, and not cause to bring forth?" says Yahweh: "shall I who cause to bring forth shut [the womb]?" says your God.