18 And [kai] another [allos] angel [aggelos] came [exerchomai] out [ek] from the altar, [thusiasterion] which had [echo] power [exousia] over [epi] fire; [pur] and [kai] cried [phoneo] with a loud [megas] cry [krauge] to him that had [echo] the
sharp [oxus] sickle, [drepanon] saying, [lego] Thrust in [pempo] thy [sou] sharp [oxus] sickle, [drepanon] and [kai] gather [trugao] the
clusters [botrus] of the vine [ampelos] of the earth; [ge] for [hoti] her [autos] grapes [staphule] are fully ripe. [akmazo] KJV-Interlinear
another angel, the one who has power over fire, came out from the altar; and he
called with a loud voice to him who had the sharp sickle, saying, "Put in
your sharp sickle, and gather the clusters from the vine of the earth, because
her grapes are ripe." NASB
The sixth angel in this vision thus far, came out of the alter. This alter is in heaven, and means sacrifice, kill, slaughter.
He had power over fire, and the fire is in reference to the intense fires of a burning alter, like a blast furnace. The fire of the alter.
Power here means privilege or authority. This angel was given authority to slaughter, or command the slaughter, in this case.
Note, only unbelievers and evil types are set for slaughter. This terminology never applies to believers, as a policy from God. God protects believers, God slaughters unbelievers and the unrighteous.
The word for ripe is a different word as was used in verse 15. This ripe, 'akmazo,' refers to fully ripe, or full to the point of bursting. However, this fullness is not of the good juices of the vine, but the iniquity of evil, bursting out to overflowing.
This describes the world as full of evil, to the bursting point, to a point beyond the maximum possible, if that were possible.
Humanity will be, in this last generation prior to the Millennium, the most corrupt, the most degenerate, the most criminal, the most applied to atrocities, the absolute worst generation of unbelieving people, in all of human history, including the pre-flood generation.
And so the slaughter will commence and as was the process of sacrificial offerings ongoing day after day, year after year in the old Testament times, so too, those last three-and-a-half years will be filled with a continuous and ongoing slaughter of unbelievers, culminating with the final slaughter in the Armageddon battle and the Second Advent.
As the world deteriorates, huge numbers of people will not see it, and they will accelerate and escalate in their evil, rather than repenting for Christ. So, simultaneously, unbelievers will commit atrocities against believers, and as we studied earlier, those who pursue will be pursued, those who kill will be killed, and the slaughter against unbelievers will likewise escalate as the atrocities against believers escalates.