four months until the harvest: Jesus referred to a common saying about farming. Farmers usually waited about four months between planting seed and gathering the crop.
In Samaria, it was likely the time of harvest, and the fields were ready to be gathered. Jesus used this picture to speak about people, not crops.
He had spoken with the woman at the well and planted spiritual seed (God’s message). Soon after, many Samaritans believed in him (4:39–42). In this way, Jesus was already gathering a harvest of faith.