In Ezekiel 26:11, this signifies the love of learning or intellectual things. (Arcana Coelestia 3727)

In Revelation 6:2, this signifies the love of understanding the Word. (Apocalypse Revealed 298)

In Zechariah 12:4, this signifies that the intellectual should be filled with falsities. (Arcana Coelestia 2383[2])

In general, 'a horse' signifies knowledge or understanding of the Word. In an opposite sense it signifies the understanding of the Word falsified by reasonings, and likewise destroyed from self-derived intelligence. 'A dead horse' signifies no understanding of truth from the Word.

833. 19:19 And I saw the beast, the kings of the earth, and their armies, gathered together to make war against Him who sat on the horse and against His army. This symbolically means that all inwardly evil people who professed faith alone will, together with their leaders and followers, attack the Lord's Divine truths in His Word and assail those who will belong to the Lord's New Church.

The beast symbolizes people caught up in a religion teaching faith alone, as may be seen in nos. 567, 576, 577, 594, 598, 601 above. That they include only those people who are inwardly evil and have professed that religion will be seen below. The kings of the earth symbolize people who more than others are caught up in the falsities of that religion, thus its leaders. For kings of the earth symbolize people governed by the church's truths from the Word, and in an opposite sense, people caught up in falsities (nos. 20, 483, 704, 737, 720, 740). Here they are people caught up in falsities. Their armies symbolize all those among them who are likewise caught up in falsities (no. 447).

To make war means, symbolically, to attack, since war in the Word symbolizes spiritual war, which is one of falsity against truth, and of truth against falsity (nos. 500, 586, 707). He that sat on the horse symbolizes the Lord in relation to the Word (nos. 820, 821). And because people cannot fight against the Lord Himself, but fight against His Divine truths found in the Word, thus fighting also against the Lord because the Lord embodies the Word, therefore this is what is meant by making war against Him who sat on the horse.

That an army or host symbolizes people who possess Divine truths, thus abstractly Divine truths themselves, accordingly people who belong to the Lord's New Heaven and New Church, because it is they who possess Divine truths, may be seen in no. 826 above.