2 “Pilate went forth again, and says unto them, Behold, I bring him forth, that you may know that I find no fault in him. Then came Jesus forth, wearing the crown of thorns and the purple robe. And he says unto them, Behold the man!” Hence it is apparent that these things were done by the soldiers not without Pilate's knowledge, whether it was that he ordered them or only permitted them, namely, for the reason we have stated above, that His enemies might all the more willingly drink in the sight of such derisive treatment, and cease to thirst further for His blood. Jesus goes forth to them wearing the crown of thorns and the purple robe, not resplendent in kingly power, but laden with reproach; and the words are addressed to them, Behold the man! If you hate your king, spare him now when you see him sunk so low; he has been scourged, crowned with thorns, clothed with the garments of derision, jeered at with the bitterest insults, struck with the open hand; his ignominy is at the boiling point, let your ill-will sink to zero. But there is no such cooling on the part of the latter, but rather a further increase of heat and vehemence.
Source: Tractates on the Gospel of John (New Advent)