That is the inner meaning of that metaphor about gathering grapes from thorns and figs from thistles in the Gospel. The thorn and the thistle, the grape and the fig, do not signify separate types of men. If so, the force of the metaphor would fail, and Necessitarian Calvinism would be established.
The thorn and the thistle are obeying God's own law of heredity and affinity by producing only thorns and thistles; they would violate the law of their being if they produced grapes and figs. It is an allegory of our separate selves, of that complex nature which differentiates us from the immanence of God as subconscious mind in the vegetable and the animal. Each man is the soil in which the "soul-man" and the "body-man" produce thorn and thistle, and the "spirit-man" produces grape and fig. The opposing functioning centres in the same individual strive for the mastery, and from this very striving emerges the perfected life of the Child of God, and that is where the possibility of what we call evil comes in. Our own limited minds teach us that God's thought-forms, imaged forth from the womb of Infinite Mind, could never attain Self-consciousness unless associated with matter in some definite form. That association with matter involved body with its "thorn and thistle" tendencies, which tendencies are the training-ground of the individual, and this training will be complete when the "spirit-man," through the "soul-man," controls the "body-man," and he can say with Paul: "I keep under my body and bring it into subjection."
As vehicles of spirit we have the capacity of living by a definite effort and purpose the higher life, the fruit-bearing life, and, as we live it, we weaken and starve the thorn-bearing life. "We are debtors," says the Apostle, we, who have received the Keys of our own Kingdom of Heaven within--"we are debtors not to live after the flesh."
No one needs the pulpit to tell them what is the life "not after the flesh." Every purposeful encouragement of the Divine nature within, every clinging to principle in time of temptation, every masterful conquest over bodily desires by forcing the mind away from sense impressions into recollection of the Divinity within, every quenching of anger by a kind and gentle word, ministers to the fruit-bearing life and withers the thorn.