Revelation 14:15

Revelation 14:15 And another angel came out of the temple, crying with a loud voice to Him who sat on the cloud, Send forth Your sickle and reap, for the hour to reap has come because the harvest of the earth is ripe. 

Footnote on "harvest"

The harvest of the earth is God's people, the believers in Christ. At His first coming to the earth, the Lord sowed Himself into His believers. All the believers since that time, who have received Him as the seed of life, have become God's crop on the earth. The first-ripe ones will be reaped as the firstfruits to God before the great tribulation. The majority will ripen with the help of the sufferings in the great tribulation and will be reaped, raptured, at the end of the great tribulation.

Footnote on "ripe"

lit. dried. To be ripe is to be "dried" of all the earthly water. The suffering of the great tribulation, like the parching sun, will dry up the earthly waters from the believers who are left on the earth in the great tribulation, enabling the believers to ripe.