A.T. Robertson Commentary Revelation 6:4

"And another [horse] came forth, a red horse: and to him that sat thereon it was given to take peace from the earth, and that they should slay one another: and there was given unto him a great sword." — Revelation 6:4 (ASV)

A red horse (ιππος πυρρος). Old adjective from πυρ (fire), flame-coloured, blood-red (2 Kings 3:22), in N.T. only here and 12:3, like Zec 1:8; 6:2 (roan horse).

To take peace from the earth (λαβειν την ειρηνην εκ της γης). Second aorist active infinitive of λαμβανω, and here the nominative case, the subject of εδοθη (see verse 2), "to take peace out of the earth." Alas, how many red horses have been ridden through the ages.

And that they should slay one another (κα ινα αλληλους σφαξουσιν). Epexegetical explanatory purpose clause with ινα and the future active of σφαζω (5:6) instead of the more usual subjunctive (verse 2). Cf. Robertson, Grammar, p. 998f. This is what war does to perfection, makes cannon fodder (cf. John 14:27) of men.

A great sword (μαχαιρα μεγαλη). Μαχαιρα may be a knife carried in a sheath at the girdle (John 18:10) or a long sword in battle as here. Ρομφαια, also a large sword, is the only other word for sword in the N.T. (Revelation 1:16; 2:12,16; Revelation 6:8; 19:15,21).