There’s a common pattern in domestic abuse cases, with the abuser professing his love and apologizing, then losing control and lashing out again, then again professing his love and sorrow, and so forth. In such cases its pretty clear that the external truth – a swinging fist – does not match the love that supposedly exists. On the other hand, when someone professes love and acts in ways that are tender and caring, the external truth – the kind actions – tend to confirm that the love is real.

That’s what the Bible means by being a "witness": It represents using what we know, the truth in front of our noses, to judge the nature of love. In this case, the witness is John, who represents the external, literal meaning of the Bible, and the "light" is divine truth brought to the world by Jesus. So John was re-establishing the Word – the laws and prophets of the Old Testament – so that Jesus could show the perfect love and truth that fill it internally. With the two in harmony, those who were willing would be able to know that Jesus was the Lord, an expression of the ultimate, creative, eternal love.

(Referenties: The Apocalypse Explained 27 [2])

1041. And ten horns. That this signifies the power of the Word from truths, is evident from the signification of horns, as denoting the power of truth against falsity; and, in the opposite sense, the power of falsity against truth (concerning which see (n. 316, 567, 776). In this case, the power of truth from the Word against falsity, because it is afterwards said:

"The ten horns, which thou sawest, are ten kings; these shall hate the whore, and shall make her desolate and naked, and shall devour her flesh, and burn her with fire; for God hath put into their hearts to give their kingdom unto the beast" (vers. 12, 16, 17).

From this it is clear that by the ten horns which the scarlet beast had, is signified the power of truth, thus of the Word, against falsities; for it is said that they shall hate the whore, and burn her with fire; and by the whore is signified the truth of the Word falsified, which in itself is falsity, and which cannot be hated and burned but by the truth of the Word in its power, thus, by those who are in truths from the Word, and account the Word only as holy, and acknowledge it as Divine truth, without regard to the dictates of the Pope. But upon this subject more will be said in what follows. The reason why there were seen ten horns is, that by ten is signified much, thus, by ten horns, much power.