I saw heaven opened: see 4.1; 11.19; 15.5.

Behold: an exclamation of surprise (see 1.7).

A white horse: see 6.2. White is the color of victory.

He who sat upon it: better, “Its rider” (see 6.2).

Faithful and True: in 3.14 Jesus is called “the faithful and true witness”; and see “the true one” in 3.7. This is a name and should be kept as concise as possible. In this context translators in certain languages will need to combine these two adjectives and say “The Trustworthy One” or “The One who Serves God Faithfully.”

In righteousness he judges and makes war: it is for a righteous cause, or governed by righteous principles, that he judges, that is, condemns, and makes war (see Isa 11.3-5). For judges see 6.10; and for makes war see 2.16. So one may also render this clause as “He uses right (or, correct) principles when he condemns people and fights against his enemies.”

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .