Gregory the Great — as excerpted in the Catena Aurea on Luke 10:1-2

“(ubi sup.) But not without deep sorrow can we add, but the labourers are few. For although there are who would hear good things, they are wanting who should spread them. Behold the world is full of priests, but seldom is there found a labourer in God’s harvest, because we undertake indeed the priestly office, but we perform not its works.”