Arcana Coelestia #3243
3243. 'All these were the sons of Keturah' means as regards matters of doctrine and the worship that sprang from these. This is clear from the meaning of 'sons' as truths and matters of doctrine, dealt with in 489, 491, 533, 1147, 2623, and from the representation of 'Keturah' as Divine Spiritual Truth joined to Divine Spiritual Good, dealt with in 3236, 3237; thus things which belong to the Lord's spiritual kingdom are meant. And because the worship of that kingdom is in accordance with matters of doctrine, therefore the sons of Keturah mean matters of doctrine, and also the worship that sprang from these.
Arcana Coelestia #1147
1147. 'And sons were born to them' means matters of doctrine deriving from those three. This is clear from the meaning of 'sons' in the internal sense as truths of faith, and also as falsities. Consequently matters of doctrine, both true and false, are meant, for such are the doctrines of Churches. That 'sons' has such a meaning, see above in 264, 489, 491, 533.