Different modes of engrafting illustrative of different kinds of conversion.
They say that engrafting is effected in four modes: one, that in which the graft must be fitted in between the wood and the bark; resembling the way in which we instruct plain people belonging to the Gentiles, who receive the word superficially. Another is, when the wood is cleft, and there is inserted in it the cultivated branch. And this applies to the case of those who have studied philosophy; for on cutting through their dogmas, the acknowledgment of the truth is produced in them. So also in the case of the Jews, by opening up the Old Testament, the new and noble plant of the olive is inserted. The third mode of engrafting applies to rustics and heretics, who are brought by force to the truth. For after smoothing off both suckers with a sharp pruning-hook, till the pith is laid bare, but not wounded, they are bound together. And the fourth is that form of engrafting called budding. For a bud (eye) is cut out of a trunk of a good sort, a circle being drawn round in the bark along with it, of the size of the palm. Then the trunk is stripped, to suit the eye, over an equal circumference. And so the graft is inserted, tied round, and daubed with clay, the bud being kept uninjured and unstained. This is the style of gnostic teaching, which is capable of looking into things themselves. This mode is, in truth, of most service in the case of cultivated trees. And “the engrafting into the good olive” mentioned by the apostle, may be [engrafting into] Christ Himself; the uncultivated and unbelieving nature being transplanted into Christ—that is, in the case of those who believe in Christ. But it is better [to understand it] of the engrafting of each one’s faith in the soul itself. For also the Holy Spirit is thus somehow transplanted by distribution, according to the circumscribed capacity of each one, but without being circumscribed.
Clement of Alexandria
The Stormata, or Miscellanies