For the flesh lusts against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other…
In material fruit-trees the sour nature of the wild plants that are grafted upon still continues in the stock or root, and is not taken away by ingrafting; it is only restrained and kept under by the graft. The nature of the graft is predominant in the tree, and overrules in bringing forth fruits according to its own kind (although with some small degree of the sour nature of the stock mixed with it), and the two natures of the graft and stock continue mixed together as long as the tree lives. This is a similitude of the state of mystical fruit-trees, and shadows forth to us this proposition: That corrupt nature abides in believers as long as they live, and is but in part subdued by grace. We find by experience that after plant is ingrafted, both the graft and the stock will shoot forth, and if the graft grow vigorously and strongly, then the shoots of the stock are but weak; but if the shoots of the stock break out strongly then the graft grows but weakly; therefore the husbandman takes pains often to cut off the shoots that grow upon the stock, so that the graft may grow the better. This is another similitude of the state of mystical fruit-trees, and shadows forth to us this proposition: That while the spiritual part in us acts and grows strongly, the fleshly part acts but weakly; so also, if the flesh be strong, the spirit is weak. This should teach us often to take notice of the actings of our spirits, whether the stock or the graft bud the faster. If we were watchful daily, and took pains with our spirits to keep them up in a spiritual frame in communion with God, then (by degrees) the shoots and growths of the spiritual part would become strong, and the shoots of the flesh weak and feeble.
Parallel VersesKJV: For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would.