John Calvin Commentary Matthew 9:37

"Then saith he unto his disciples, The harvest indeed is plenteous, but the laborers are few." — Matthew 9:37 (ASV)

The harvest is indeed abundant. By this metaphor, he intimates that many of the people are ripe for receiving the gospel. Though the greater number afterwards rejected basely and with vile ingratitude the salvation offered to them, yet the limited number of the elect, who were mixed with unbelievers, is compared to an abundant harvest, because God values a small band of his own people more highly than the rest of the world.

Though at that time many assumed this character, yet because few of them discharged it faithfully, he does not rank them among laborers: for he employs the word laborers in a good sense.

When Paul complains (2 Corinthians 2:13) of bad laborers, he refers to their boasting: for he would not have bestowed the designation of laborers⁵³⁴ on those who devoted all their exertions to ruin and waste the flock, had it not been that they gloried in the false pretense.

⁵³⁴ ἐργάται δόλιοι, deceitful workmen.