The Gospel of John alone records the foot-washing, Jesus' final words to the disciples, and the High-Priestly Prayer, chapters 13-17. In our text Judas has just left and Jesus begins the discourse found in chapters 13-16.
Westcott: This first section of the Lord's final revelation of Himself and of His work contains in germ the main thoughts which are afterwards unfolded. He declares His victory (verses 31 and 32), His departure (verse 33), the characteristic of His Society (verses 34 and 35). The central idea is that of separation, its nature, its necessity, its consequences.
"When" means "just now." Judas thought that he would be victorious in betraying Jesus, but the very opposite is true. Jesus is victoriously saying that He has just been glorified in actual victory over Judas and all evil. Some commentators take the aorist passive verb in verse 31 as complexive, referring to the whole passion, death, resurrection, and ascension. Still others take the aorists of the entire past ministry of Jesus. In any case, Jesus and Father had been glorified in Jesus' Incarnation, Luke 2:14, the miracles, John 2:11, by Jesus' active and passive obedience, John 12:28.
Verses 31 and 32 make plain that Jesus and the Father were glorified, clothed in splendor, both in Jesus' humiliation and exaltation, Philippians 2:5-11. Whether we limit verse 31 to the incident with Judas, a declaration of victory before the battle, or make it complexive covering everything from this point on, makes little difference.
Note that Jesus speaks of Himself as the Son of man, the God-man who took our place. That Jesus is true God is implicit in this verse. What is emphasized is the note of victory midst great sorrow and sadness.
Note that the protasis, or first part of this verse, "If God is glorified in him," is not found in the best manuscripts. However all our translations have it, except Beck. Westcott and Lenski omit it. Some commentaries retain it, enclosing it in brackets. It is the protasis of a fact or particular condition. The meaning: "If (as I maintain) God has been glorified in Him, etc." If we omit the protasis, we should put a "furthermore" before "God will glorify the Son." If we retain the protasis, then we should put an "also."
The first "him" refers to Christ, the "him" is reflexive and refers to God. The point is that Jesus knows full well, though the prospect is so dark and gloomy, that He is true God and that God stands fully behind Him in gaining the victory and eventual glorification.
"My children" occurs only here in all four Gospels. It denotes endearment. It likely also indicates the disciples' immaturity and weakness.
"A little longer" means that just a few hours more and the association which the disciples have known for three years will come to an end. On this verse look at John 7:34 and John 8:21.
Both the Jews and Jesus' disciples would seek Him. Neither would be able to come where he is about to be. But there is a great difference. Jesus warns the Jews that they will die in their sins whereas Jesus is preparing and comforting the disciples. Jesus tells the Jews that they will not find Him but He comforts the disciples by saying that eventually they will come to Him, John 12:26; John 14:3; John 17:24.
For the Jews this statement is Law. For the disciples it is preparation and comfort. Their old way of life with Him is now over.
Westcott: 'Ye shall seek me' in the coming times of trial after the Passion, and after the Resurrection, and after the Ascension, and even to the consummation of the age, in the manifold loneliness of toil. Look at Luke 17:22.
But Lutheran commentators stress the fact that Jesus removed merely His visible presence. He was still with them. Look at John 14:16-18.
The thought here is closely connected to the preceding. "Command" is in the sense of "precept," "order" might be too harsh. Jesus says: "Just as I have loved you" and the meaning of this is obvious. See Galatians 2:20.
Never before had mankind thus witnessed Jesus' love for man. Jesus' love for man makes everything new, fulfilled. In the evening when Jesus spoke these words the disciples had displayed selfishness rather than love. He got down and washed their feet and told them to serve each other like that, see verses 14-15. Luke 22:24 tells us that there was strife because they were arguing about who was the greatest. Jesus says that His love is constant and continuous. Look at Galatians 2:20 again. He is speaking about what He did in their stead, in their place, not how He feels about them. Of course, as a result of this He constantly loves them.
"All men" includes all people, both believers and unbelievers. It makes unbelievers stop and think. It strengthens the believers. "Will know" means that this knowledge comes from the outside. "My disciples" lays stress on the fact that they belong to Jesus. By the way, all Christians are disciples of Jesus, learners of His. The mutual love of Christians attracts people, eventually, to the Lord. Note that Jesus says "are," not "will be." The tense of this verb presents a condition that Jesus expects to happen.
The second part of this verse flows naturally from the first part.
In verses 34 and 35 the constant mutual love of Christians is mentioned three times. Beck translates: "By your loving one another everybody will know, etc."
Tertullian: (Writing in about 200 AD) But it is mainly the deeds of a love so noble that lead many to put a brand upon us. 'See' they say 'how they love one another' for they themselves are animated by mutual hatred; 'see how they are ready even to die for one another' for they themselves will rather put to death.
Westcott: Chrysostom drew a remarkable picture of the divisions of Christians as hindering the conversion of the heathen.
Lenski: Minucius Felix declared with regard to the Christians 'They love each other even without being acquainted with each other.'