Many of Jesus' parables are enigmatic, which Jesus acknowleged. They "veiled" the truth from those who were disinterested, as a judgment. But here, Jesus provides an explanation which serves as the key to unlocking his other parables of the kingdom. Essentially, he says that participation in the future fullness of Christ's kingdom requires present possession of the Spirit, who is the "downpayment" of the age to come, which is evidenced by fruitfulness. It is not enough to hear his teachings, but one must walk in them by faith.