From: John 16:29-33
Fullness of Joy (Continuation)
 His (Jesus') disciples said, "Ah, now You are speaking plainly, not in any figure!  Now we know that You know all things, and need none to question You; by this we believe that You came from God."  Jesus answered them, "Do you now believe?  The hour is coming, indeed it has come, when you will be scattered, every man to his home, and will leave Me alone; yet I am not alone, for the Father is with Me.  I have said this to you, that in Me you may have peace. In the world you have tribulation; but be of good cheer, I have overcome the world."
25-30. As can be seen also from other passages in the Gospels, Jesus spent time explaining His doctrine in more detail to His Apostles than to the crowd (cf. Mark 4:10-12 and paragraph)--to train them for their mission of preaching the Gospel to the whole world (cf. Matthew 28:18-20). However, our Lord also used metaphors or parables when imparting instruction to the Apostles, and He does so in this discourse of the Last Supper--the vine, the woman giving birth, etc.: He stimulates their curiosity and they, because they do not understand, ask Him questions (cf. verses 17-18). Jesus now tells them that the time is coming when He will speak to them in a completely clear way so that they will know exactly what He means. This He will do after the Resurrection (cf. Acts 1:3). But even now, since He knows their thoughts, He is making it ever plainer to them that He is God, for only God can know what is happening inside someone (cf. 2:25). Verse 28, "I came from the Father and have come into the world; again, I am leaving the world and going to the Father" summarizes the mystery of Christ's Person (cf. John 1:14; 20:31).
31-32. Jesus moderates the Apostles' enthusiasm, which expresses itself in a spontaneous confession of faith; He does this by asking them a question which has two dimensions. On the one hand, it is a kind of reproach for their having taken too long to believe in Him: it is true that there were other occasions when they expressed faith in the Master (cf. John 6:68-69; etc.), but until now they have not fully realized that He is the One sent by the Father. The question also refers to the fragility of their faith: they believe, and yet very soon they will abandon Him into the hands of His enemies. Jesus requires us to have a firm faith: it is not enough to show it in moments of enthusiasm, it has to stand the test of difficulties and opposition.
33. The Second Vatican Council teaches in connection with this passage: "The Lord Jesus who said `Be of good cheer, I have overcome the world' (John 16:33), did not by these words promise complete victory to His Church in this world. This sacred Council rejoices that the earth which has been sown with the seed of the Gospel is now bringing forth fruit in many places under the guidance of the Spirit of the Lord, who is filling the world" ("Presbyterorum Ordinis", 22).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.