Don't you say, 'There are yet four months until the harvest?' Behold, I tell you, lift up your eyes, and look at the fields, that they are white for harvest already.
The disciples needed spiritual vision. They could obtain it by lifting their eyes and looking on the fields of lost people rather than being completely absorbed in their physical needs. As with physical grain, the opportunity for harvesting spiritually is relatively brief. If left unreached, people die in their sins.