‘And another angel came out from the Temple which is in Heaven, he also having a sharp sickle, and another angel came out from the altar, he who has power over fire, and he called with a great voice to him who had the sharp sickle, saying, “Send forth your sharp sickle and gather the clusters of the vine of the earth, for her grapes are fully ripe”.'
John is at pains to demonstrate that He Who sits on the throne is at one with the Son of Man in the action about to take place, for the angel with the sickle comes forth from His Temple. He is to help with the reaping.
The angel from the altar who has power over fire was described in Revelation 8:5. He represents the prayers of God's people and here we find that this final hour of judgment is in response to those prayers (Luke 18:7; Revelation 6:10). Creation itself has groaned and waited (Romans 8:19-22). Now its hour too has come. This is intrinsic in the Lord's prayer. ‘May your name be hallowed, your rule come, your will be done' (Matthew 6:9-10). They were prayers for the fulfilment of God's purposes.
The angels are the assistants of the Son of Man in judgment. The Son of Man initiates the reaping, the angels carry it out and gather the remains of the harvest to be burned (Matthew 13:40-42). This is assumed here and illustrated by the treatment of the vintage. John sees the two harvests as taking place at the same time. The emphasis is on the fact that nothing is excluded.