In "Word Focus" Darrell Grimm writes:
The contrast between the branches is illustrated in the husbandman's actions toward each. The word translated as husbandman not only indicates ownership but labor as well. So Christ said that “He,” the Father, cuts away those who bear no fruit. Christians are not fruitless because of some defect in their graft to the Vine, but because of the choice of their free will. Likewise the fruitful branch is so because of a desire to be so. Instead of being cut away completely, this branch undergoes a pruning which cuts away all that hinders fruitfulness. This pruning has been likened to the experience of sanctification. The heart must be purged of the old nature, or stunted growth and unfruitfulness will follow.
Discussion: Fruit is a natural by-product of a healthy tree or vine. If a Christian is unfruitful spiritually, what does that say about his or her heart?
Source: Jesus, Son of God: Adult Teacher's Insights, page 58.