Under the altar (υποκατω του θυσιαστηριου). "Under" (υποκατω), for the blood of the sacrifices was poured at the bottom of the altar (Leviticus 4:7). The altar of sacrifice (Exodus 39:39; Exodus 40:29), not of incense. The imagery, as in Hebrews, is from the tabernacle. For the word see Matthew 5:23, often in Rev. (Revelation 8:3; Revelation 8:5; Revelation 9:13; Revelation 11:1; Revelation 14:18; Revelation 16:7). This altar in heaven is symbolic, of course, the antitype for the tabernacle altar (Hebrews 8:5). The Lamb was slain (Revelation 5:6; Revelation 5:9; Revelation 5:12) and these martyrs have followed the example of their Lord.

The souls (τας ψυχας). The lives, for the life is in the blood (Leviticus 17:11), were given for Christ (Philippians 2:17; 2 Timothy 4:6).

Of the slain (των εσφαγμενων). See Revelation 5:6. Christians were slain during the Neronian persecution and now again under Domitian. A long line of martyrs has followed.

For the word of God (δια τον λογον του θεου). As in Revelation 1:9, the confession of loyalty to Christ as opposed to emperor-worship.

And for the testimony which they held (κα δια την μαρτυριαν ην ειχον). See also Revelation 1:9. Probably κα equals "even" here, explaining the preceding. The imperfect tense ειχον suits the repetition of the witness to Christ and the consequent death.