According to John, this verse means an angel is asking for the grapes on earth to be picked because they are ready. It's like saying it's time to gather something because it is finished growing.
Revelation 14:18: And another angel came out from the altar, which had power over fire; and cried with a loud cry to him that had the sharp sickle, saying, Thrust in thy sharp sickle, and gather the clusters of the vine of the earth; for her grapes are fully ripe.
Revelation 14:18 describes an angel in charge of fire calling for grapes to be gathered for the winepress of God's wrath. The moral conflict here could be the portrayal of divine wrath and judgment, which might contrast with teachings of mercy and forgiveness found elsewhere in the Bible. This can seem inconsistent with the idea of a loving and forgiving God.