Arcana Coelestia#4821
4821. 'And she conceived and bore a son' means that from this came the falsity of the Church. This is clear from the meaning of 'conceiving and bearing' as acknowledging in faith and action, dealt with in 3905, 3915, 3919, and from the meaning of 'a son' as the truth of the Church, but in the contrary sense falsity, dealt with in 489, 491, 533, 1147, 2623, 3373, 4257. Consequently 'she conceived and bore a son' here means that the Church among the tribe of Judah acknowledged falsity in faith and action. The reason this son means the falsity of the Church is that he was the firstborn, and in the Ancient Churches 'the firstborn' meant the truth of faith, 352, 3325, and so in the contrary sense falsity, which was also the meaning of the firstborn among men and the firstborn among beasts in Egypt, 3325. The fact that truth is not meant but falsity is evident from what follows shortly, for in verse 7 it says, 'Er, Judah's firstborn, was evil in the eyes of Jehovah, and Jehovah caused him to die'. Er, this son's name, also implies the particular nature of this falsity, even as Onan, his second son's name, implies the particular nature of that meant by him, namely what is wrong or evil.
Arcana Coelestia#2623
2623. 'A son' means the Divine Rational. This is clear from the meaning of 'a son'. In the internal sense of the Word 'a son' means truth, 489, 491, 533; and because truth is the principal element in the rational, 2072, 2189, 'a son' also means the rational. But here the Divine Rational is meant in which the principal element is good. 'Isaac' too, to whom 'a son' refers, represents this good, as will be shown further on.