A crab tree will never yield pleasant fruit, until you change the nature of it. Take a crab tree and plant it in the best soil that you have, and water it, and dress it, and prune it as much as you can, yet this crab tree will bear nothing but crabs, sour fruit, until you come to graft it; and then your grafting of it changes the nature of the stock, and it has another principle, and so then it brings forth good fruit. … Take the best natured person in the world and plant him in the best soil, in the best ground, in church ground; plant him in the house of God, and there let him be watered by holy doctrine, and let him be cultivated every day, but still he will bring forth nothing but unsavory fruit, until he himself is changed. Though he is under all those spiritual means, yet until those means have wrought effectually in him, his actions are all unsavory.
It is only by our implantation into Jesus Christ that we become fit to do good that is acceptable to God.
It is this that makes the change. For as in nature the graft changes the stock, so in grace, the stock changes the grafted branch. As we are grafted into Christ, He changes the branch; being planted into Christ, by the power of the Spirit, we are then made like Him, and then we shall bring forth fruits of righteousness, which are to the glory of God.