'Sons of the stranger' signify counterfeit truths, or falsities. 'Our sons' signify the doctrines of truth, and 'our daughters,' the doctrines of good, as in Psalm 144:11-12.

(References: Arcana Coelestia 489; Psalms 144:11)

217. That in the Word 'vine' means spiritual good and 'fig' natural good is totally unknown nowadays because the internal sense of the Word has been lost. Nevertheless this is what vine and fig mean or embody whenever they occur, as with the Lord's statements in His parables involving a vineyard and also a fig tree, and in the incident recorded in Matthew,

Jesus seeing a fig tree by the wayside went to it but found nothing on it but leaves only; therefore He said to it, Let no fruit from now on ever be born from you! Therefore the fig tree withered at once. Matthew 21:19.

This meant that no good, not even natural good, was found on earth. 'Vine' and 'fig' have the same meaning in Jeremiah,

Were they ashamed that they committed abomination? No indeed, they were not at all filled with shame and they did not know how to blush. Therefore I will surely gather them, says Jehovah; there will be no grapes on the vine, nor figs on the fig tree; and its leaf has fallen. Jeremiah 8:12-13.

This means that all good, both spiritual and natural, had perished, for people were such that they were not even capable of being filled with shame, just as nowadays people governed by evil are so brazen that they even boast about that evil. In Hosea,

Like grapes in the wilderness I found Israel; like the first fruit on the fig tree, in the beginning, I saw your fathers. Hosea 9:10.

And in Joel,

Fear not, you beasts of my fields, for the tree will bear its fruit, the fig tree and the vine will give their full yield. Joel 2:22.

'Vine' stands for spiritual good, 'fig' for natural good.