Matthew 26:49

If it be asked why Judas betrayed Jesus with a kiss, according to some it was because He desired to keep up the reverence due to his Master, and did not dare to make an open assault upon Him; according to others, it was out of fear that if he came as an avowed enemy, he might be the cause of His escape, which he believed Jesus had it in His power to effect. But I think that all betrayers of truth love to assume the guise of truth, and to use the sign of a kiss. Like Judas also, all heretics call Jesus Rabbi, and receive from Him mild answer.

But wherefore doth He say this? Because often when seized by them He had gone out through the midst, without their knowing it. Nevertheless, then also this would have been done, if it had not been His own will that He should be taken. It was at least with a view to teach them this, that He then blinded their eyes, and Himself asked, "Whom seek ye?" And they knew Him not, though being with lanterns and torches, and having Judas with them. Afterwards, as they had said, "Jesus;" He saith, "I am He" whom ye seek: and here again, "Friend, wherefore art thou come?" For after having shown His own strength, then at once He yielded Himself. But John saith, that even to the very moment He continued to reprove him, saying, "Judas, betrayest thou the Son of Man with a kiss?" Art thou not ashamed even of the form of the betrayal? saith He. Nevertheless, forasmuch as not even this checked him, He submitted to be kissed, and gave Himself up willingly; and they laid their hands on Him, and seized Him that night on which they ate the passover, to such a degree did they boil with rage, and were mad. However, they would have had no strength, unless He had Himself suffered it. Yet this delivers not Judas from intolerable punishment, but even more exceedingly condemns him, for that though he had received such proof of His power, and lenity, and meekness, and gentleness, he became fiercer than any wild beast.

The Lord suffered the traitor's kiss, not to teach us to dissemble, but that He might not seem to shrink from His betrayal.

(non occ.) Having said above that the Lord offered Himself of His own accord to His pursuers, the Evangelist proceeds to relate how He was seized by them.

(Serm. de Symb. ad Catech. 6.) Exult, Christian, you have gained by this bargain of your enemies; what Judas sold, and what the Jews bought, belongs to you.