Therefore said he unto them, The harvest truly is great, but the labourers are few: pray ye therefore the Lord of the harvest, that he would send forth labourers into his harvest. This and many of the sayings reported on this occasion had been said apparently before, when the twelve had been sent out on a similar mission.
It seems almost certain that, on several occasions, the Lord repeated the same expressions containing great truths, with scarcely any variation in language. The harvest simile was evidently a favourite one of the Master.
"The field is the world" he told them in the parable of the sower. It is reproduced by St. John (Revelation 14:14-19).