John 13:25

When Christ had said, one of you is to betray me, St. Peter whispered with St. John, by turning to him behind Jesus’s back, and desired him to ask, who this was: now when John had leaned down upon the breast of Jesus, or as the Greek hath it, falling down on the breast of Jesus, as a person may do in a great concern, or fit of grief, he said, Lord, who is it? This posture seems to have been only for that moment of whispering, and to have been different from the posture of eating at table. (Witham)

3. The question was asked accordingly (v. 25): He then, lying at the breast of Jesus, and so having the convenience of whispering with him, saith unto him, Lord, who is it? Now here John shows, (1.) A regard to his fellow-disciple, and to the motion he made. Though Peter had not the honour he had at this time, yet he did not therefore disdain to take the hint and intimation he gave him. Note, Those who lie in Christ's bosom may often learn from those who lie at his feet something that will be profitable for them, and be reminded of that which they did not of themselves think of. John was willing to gratify Peter herein, having so fair an opportunity for it. As every one hath received the gift, so let him minister the same for a common good, Rom 12 6. (2.) A reverence of his Master. Though he whispered this in Christ's ear, yet he called him Lord; the familiarity he was admitted to did not at all lessen his respect for his Master. It becomes us to use a reverence in expression, and to observe a decorum even in our secret devotions, which no eye is a witness to, as well as in public assemblies. The more intimate communion gracious souls have with Christ, the more sensible they are of his worthiness and their own unworthiness, as Gen 18 27.

Verses 18-30 Our Lord had often spoken of his own sufferings and death, without such trouble of spirit as he now discovered when he spake of Judas. The sins of Christians are the grief of Christ. We are not to confine our attention to Judas. The prophecy of his treachery may apply to all who partake of God's mercies, and meet them with ingratitude. See the infidel, who only looks at the Scriptures with a desire to do away their authority and destroy their influence; the hypocrite, who professes to believe the Scriptures, but will not govern himself by them; and the apostate, who turns aside from Christ for a thing of naught. Thus mankind, supported by God's providence, after eating bread with Him, lift up the heel against Him! Judas went out as one weary of Jesus and his apostles. Those whose deeds are evil, love darkness rather than light.