The title is taken from Matthew 13. Jesus was speaking to the people in parables. His disciples took him aside and asked him to explain the parable of the weeds,(Matthew 13: 38-43). "The weeds are the sons of the evil one, and the enemy who sowed them is the devil. The harvest is the end of the age, and the reapers are angels.
The Harvest of the Earth is repeated in Revelation 14.
"Then I looked and behold a white cloud, and seated on the cloud one like a son of man, with a golden crown on his head, and a sharp sickle in his hand. And another angel came out of the temple calling with a loud voice to him who sat on the cloud, "Put in your sickle, and reap, for the hour to reap has come, for the harvest of the earth is fully ripe. So he who sat on the cloud swung his sickle across the earth and the earth was reaped."