The following passages show that spiritually understood, “adultery” means polluting what is good in the Word and distorting what is true in it:
Babylon has made all nations drink of the wine for her fornication. (Revelation 14:8)
An angel said, “I will show you the judgment of the great whore who sits on many waters, with whom the kings of the earth committed fornication.” (Revelation 17:1-2)
Babylon has made all nations drink of the wine of the wrath of her fornication, and the kings of the earth have committed fornication with her. (Revelation 18:3)
God has judged the great whore who corrupted the earth with her fornication. (Revelation 19:2)
Fornication is associated with Babylon because Babylon means people who claim the Lord’s divine power for themselves and profane the Word by polluting and distorting it. That is why Babylon is called “the Mother of Fornications and the Abominations of the Earth” in Revelation 17:5.
Fornication means much the same in the prophets—in Jeremiah, for example:
In the prophets of Jerusalem, I have seen appalling obstinacy; they commit adultery and walk in a lie. (Jeremiah 23:14)
Two women, daughters of one mother, played the whore in Egypt; in their youth they behaved wantonly. The first was unfaithful to me and took delight in lovers from neighboring Assyria. Upon them, too, she bestowed her acts of whoredom, but without giving up her wantonness in Egypt. The second became more corrupt in her love than the first, and her acts of whoredom were worse than her sister’s. She increased her whoredom and made love to Chaldeans; sons of Babel came to her, into the bed of love, and defiled her with their debauchery. (Ezekiel 23:2-17)
This is about the church of Israel and Judah, who are the “daughters of one mother” in this passage. Their acts of whoredom mean their pollutions and distortions of the Word, and since in the Word Egypt means factual knowledge, Assyria reasoning, Chaldea the profanation of what is true, and Babel the profanation of what is good, it says that they committed acts of whoredom with those countries.
Much the same is said in Ezekiel of Jerusalem, meaning the church in respect to its teachings:
Jerusalem, you trusted in your own beauty, and played the whole because of your fame, even to the point that you poured out your whoredom on everyone who passed by. You played the whore with the Egyptians, your very fleshly neighbors, and increased your acts of whoredom. You played the whore with Assyrians, because you were insatiable; indeed played whore with them. You multiplied your acts of whoredom as far as the land of the trader, Chaldea. An adulterous wife takes strangers instead of her husband. All make payment to their whores, but you made payments to all your lovers to come to you from all around for your whoredom. Now then, O whore, hear the Word of Jehovah. (Ezekiel 16:15, 26, 28-29, 32-33, 35, and following)
On Jerusalem meaning the church, see Teaching on the Lord 62, 63. Fornication means much the same in Isaiah 23:17-18; 57:3; Jeremiah 3:2, 6, 8-9, 5:7; 29:23; Micah 1:7; Nahum 3:4; Hosea 4:7, 10-11; also Leviticus 20:5; Numbers14:33; 15:39; and elsewhere.
That is why the Lord called the Jewish nation “an adulterous generation” (Matthew 12:39; 16:4; Mark 8:38).
from Life/Faith, Section 79