Jesus has promised to speak plainly, and the disciples think he has now done so (v. 29). The climactic affirmation in verses 27-28 is indeed quite clear. Jesus has just said that they believe that he has come from God (v. 27), and they affirm that faith, basing it on their knowledge (oidamen, "we know"; NIV, we can see) that you know all things and that you do not even need to have anyone ask you questions (v. 30). Their reference to questions may seem backward. If someone knows something, then we would say he or she does not need to ask questions. The idea here, however, is that "the ability to anticipate questions and not to need to be asked is a mark of the divine" (Brown 1970:725-26; cf. Mt 6:8; Josephus Antiquities of the Jews 6.230). As the one sent from God, Jesus' knowledge is complete; thus one can trust him and not fret over the questions one might have. His revelation has validated his claim to be the one sent from God. Our knowledge of his identity grounds our faith in him, both in the sense of belief about him and trust in him.
Earlier, in the face of very cryptic teaching, Peter had made essentially the same statement: "We believe and know that you are the Holy One of God" (6:69). Despite this affirmation the disciples have been full of questions until now, when they think they finally get it. But they have not yet seen the cross, and therefore they do not yet know the Father's heart of love revealed in the laying down of the Son's life. So in fact their expression of knowledge reveals their ignorance. How often even today, with the new birth and the Spirit, we think we have something figured out, only to have God reveal to us yet further riches about himself and the life he shares with us.
So Jesus, in his love for them, must give them a reality check. His statement You believe at last! (v. 31) could actually be a question, "Now you believe?" But Jesus is not doubting their faith. Instead he is telling them they have not yet taken the final exam for this course, so their celebrations are premature. Their faith will be tested and deepened enormously in the next few days. Everyone of them, without exception, will be scattered (v. 32; cf. Zech 13:7). John himself will return to Jesus and be at the cross, but he, like Peter, will not remain close enough to Jesus to be in harm's way (see comments on 18:12-14; cf. Carson 1991:549). They will all be scattered until they are gathered again beyond the cross by the resurrected one, after the "little while."
They will all abandon Jesus, but the Father will still be with him (v. 32). How does this correspond to Jesus' cry of abandonment on the cross, "My God, my God, why have you forsaken me?" (Mt 27:46; Mk 15:34)? When Jesus took our sin upon himself on the cross, he who had always known complete intimacy with the Father experienced, for the first time, the gulf that separates God from sin, light from darkness. But something deeper was also at work. This abandonment and its experience do not mean Jesus lacked faith in God. In fact, the cry of abandonment is a quote from the beginning of Psalm 22, "and the whole meaning of the Psalm is that God does not desert His suffering servants" (Hoskyns 1940b:582). His cry expresses both the reality of what he was undergoing and his faith in its outcome. If Abraham could offer up Isaac in the hope of resurrection (Gen 22; Heb 11:17-19), how much more could Jesus have confidence in God, whom he knew far better than Abraham did, and in the power of God's life, which he understood far better than Abraham did. Rather than contradicting the Synoptic accounts, Jesus' statement in verse 32 helps us interpret them correctly (cf. Hoskyns 1940b:582).
While Jesus must warn the disciples that the suffering is far from over, he does not end on that note. Now, as he has throughout the farewell discourse, Jesus warns them ahead of time so they will be prepared. He has told them not to let their hearts be troubled (14:1) but to receive his peace (14:27). This peace, as he now emphasizes (v. 33), is found in him, not in the world. The world will give them trouble, that is, the opposition that comes from those who are in rebellion against God (thlipsis; cf. v. 21). But they can take heart because he has overcome the world; he has met it in battle and conquered it (nenikeka). The theme of conflict has been present throughout the Gospel, since the beginning of the prologue (1:5), but this is the only place this word occurs. The peace and salvation spoken of throughout the Gospel all depend on his having conquered. His conquest, in turn, enables the disciples themselves to conquer the evil one, as John stresses in his first letter (1 Jn 2:13-14; 4:4; 5:4-5; cf. Rev 2:7, 11, 17, 26; 3:5, 12, 21; 21:7). Thus, this is indeed a fitting line for the conclusion of Jesus' teaching.
Until death itself becomes a revelation of God the disciples can be troubled in the world, the place of death. Their joy cannot be stable and secure until they see him again (v. 16, 19) and he sees them (v. 22). Then will they reap the benefits of his conquest by becoming one with him as he pours out the Spirit. They will not ask him, but rather they will be one with him, asking the Father in his name. So their joy will be full—the joy of union with God in Christ by the Spirit. They will know God's glory and will manifest his glory as they, in union with the living Christ by the Spirit, bear fruit as Jesus did, asking for what Jesus did. Their focus and source will be God, and thus they will have peace no matter what the world may throw at them.