A.T. Robertson Commentary Revelation 20:4

"And I saw thrones, and they sat upon them, and judgment was given unto them: and [I saw] the souls of them that had been beheaded for the testimony of Jesus, and for the word of God, and such as worshipped not the beast, neither his image, and received not the mark upon their forehead and upon their hand; and they lived, and reigned with Christ a thousand years." — Revelation 20:4 (ASV)

And they sat upon them (κα εκαθισαν επ' αυτους). First aorist active indicative of καθιζω. Another period here apparently synchronous (verse 7) with the confinement of Satan in the abyss. No subject is given for this plural verb. Apparently Christ and the Apostles (Matthew 19:28; Luke 22:30) and some of the saints (1 Corinthians 6:3), martyrs some hold.

Judgment was given unto them (κριμα εδοθη αυτοις). First aorist passive of διδωμ. Picture of the heavenly court of assizes.

The souls (τας ψυχας). Accusative after ειδον at the beginning of the verse.

Of them that had been beheaded (των πεπελεκισμενων). Genitive of the articular perfect passive participle of πελεκιζω, old word (from πελεκυς an axe, the traditional instrument for execution in republican Rome, but later supplanted by the sword), to cut off with an axe, here only in N.T. See 6:9; 18:24; 19:2 for previous mention of these martyrs for the witness of Jesus (1:9; 12:17; 19:10). Others also besides martyrs shared in Christ's victory, those who refused to worship the beast or wear his mark as in 13:15; 14:9ff.; 16:2; 19:20.

And they lived (κα εζησαν). First aorist active indicative of ζαω. If the ingressive aorist, it means "came to life" or "lived again" as in 2:8 and so as to verse 5. If it is the constative aorist here and in verse 5, then it could mean increased spiritual life. See Joh 5:21-29 for the double sense of life and death (now literal, now spiritual) precisely as we have the second death in Re 2:11; 20:6,14.

And reigned with Christ (κα εβασιλευσαν μετα του Χριστου). Same use of the first aorist active indicative of βασιλευω, but more clearly constative. Beckwith and Swete take this to apply solely to the martyrs, the martyrs' reign with Christ.