The harvest, of course, is a spiritual one. This is a harvest of God s crop, which is prepared by Him. The rich harvest, that is said to be plentiful, refers to the people who are farmed by Christ. By using this agricultural metaphor, Jesus implies that God is in charge of making the crop grow. Once the crop is mature and grown, it is harvest time.
Missionaries are such reapers who harvest the crop.
We are promised upon Jesus own authority that the harvest will not be a slender one. Note also that Jesus speaks in the present tense. It is not just in the future that the harvest will be plentiful, but right now. As we sit comfortably in an American church, at this very moment there is somewhere God s mission field, some ripe fruit ready to be harvested. The harvest is plentiful.