Celsus, moreover, thinks that we have invented this “tree of life” to give an allegorical meaning to the cross; and in consequence of his error upon this point, he adds: “If he had happened to be cast down a precipice, or shoved into a pit, or suffocated by hanging, there would have been invented a precipice of life far beyond the heavens, or a pit of resurrection, or a cord of immortality.” And again: “If the 'tree of life' were an invention, because he— Jesus— (is reported) to have been a carpenter, it would follow that if he had been a leather-cutter, something would have been said about holy leather; or had he been a stone-cutter, about a blessed stone; or if a worker in iron, about an iron of love.”
Now, who does not see at once the paltry nature of his charge, in thus calumniating men whom he professed to convert on the ground of their being deceived? And after these remarks, he goes on to speak in a way quite in harmony with the tone of those who have invented the fictions of lion-like, and ass-headed, and serpent-like ruling angels, and other similar absurdities, but which does not affect those who belong to the Church. Of a truth, even a drunken old woman would be ashamed to chaunt or whisper to an infant, in order to lull him to sleep, any such fables as those have done who invented the beings with asses' heads, and the harangues, so to speak, which are delivered at each of the gates.
But Celsus is not acquainted with the doctrines of the members of the Church, which very few have been able to comprehend, even of those who have devoted all their lives, in conformity with the command of Jesus, to the searching of the Scriptures, and have laboured to investigate the meaning of the sacred books, to a greater degree than Greek philosophers in their efforts to attain a so-called wisdom.
Source: Against Celsus (New Advent)