Revelation 6:9

9. Under the altar The altar of the temple in Revelation 11:1, namely, of the scenic earthly Jerusalem. Note Revelation 4:11. It is not the altar of incense, but the grand altar of sacrifice. The law was, The whole blood of the bullock shall be poured at the bottom of the altar of burnt-offering, which is before the tabernacle of the congregation.

Leviticus 4:7. And as the blood is the animal soul or life, so symbolically the souls of those who had been sacrificed for their faith are represented as lying below the altar, and crying to God for retribution. Not that the blood symbolizes souls, but the souls themselves are seen, shadowy forms, by the seer’s spiritual eye. Hengstenberg maintains that souls here means, not the disembodied spirits of the martyrs, but their blood, which cries for vengeance, poetically, like the blood of Abel. But how could blood speak of avenging our blood? Hengstenberg’s evasion, that it is the slain who thus speak, is inadmissible. Where were the slain, as seen by John, crying, if they were not the souls? Alford and Elliott both interpret this of really disembodied souls whose condition symbolizes the repression of the cause of Christ under power of antichrist. And yet, in Revelation 20:4, where these same souls reappear to reign, as symbol of the triumph of Christ over antichrist, these interpreters maintain the souls of the beheaded martyrs to be their bodies!