The Gospel for the Ascension of Our Lord can be viewed here.
From: John 17:11b-19
The Priestly Prayer of Jesus (Continuation)
(Jesus lifted his eyes to heaven and said, ) [11b] "Holy Father, keep them in thy name, which thou has given me, that they may be one, even as we are one.  While I was with them, I kept them in thy name, which thou hast given me; I have guarded them, and none of them is lost but the son of perdition, that the scripture might be fulfilled.  But now I am coming to thee; and these things I speak in the world, that they may have my joy fulfilled in themselves.  I have given them thy word; and the world has hated them because they are not of the world.  I do not pray that thou shouldst take them out of the world, but that thou shouldst keep them from the evil one.  They are not of the world, even as I am not of the world.  Sanctify them in the truth; thy word is truth.  As thou didst send me into the world, so I have sent them into the world.  And for their sake I consecrate myself, that they also may be consecrated in truth.
11-19. Jesus now asks the Father to give his disciples four things--unity, perseverance, joy and holiness. By praying him to keep them in his name (v. 11) he is asking for their perseverance in the teaching he has given them (cf. v. 6) and in communion with him. An immediate consequence of this perseverance is unity: "that they may be one, even as we are one"; this unity which he asks for his disciples is a reflection of the unity of the three divine Persons.
He also prays that none of them should be lost, that the Father should guard and protect them, just as he himself protected them while he was still with them. Thirdly, as a result of their union with God and perseverance they will share in the joy of Christ (v. 13): in this life, the more we know God and the more closely we are joined to him, the happier will we be; in eternal life our joy will be complete, because our knowledge and love of God will have reached its climax.
Finally, he prays for those who, though living in the world, are not of the world, that they may be truly holy and carry out the mission he has entrusted to them, just as he did the work his Father gave him to do.
12. "That the scripture might be fulfilled": this is an allusion to what he said to the Apostles a little earlier (Jn 13:18) by directly quoting Scripture: "He who ate my bread has lifted his heel against me" (Ps 41:10). Jesus makes these references to Judas' treachery in order to strengthen the Apostles' faith by showing that he knew everything in advance and that the Scriptures had already foretold what would happen.
However, Judas went astray through his own fault and not because God arranged things that way; his treachery had been taking shape little by little, through his petty infidelities, and despite our Lord helping him to repent and get back on the right rode (cf. note on Jn 13:21-32); Judas did not respond to this grace and was responsible for his own downfall. God, who sees the future, predicted the treachery of Judas in the Scripture; Christ, being God, knew that Judas would betray him and it is with immense sorrow that he now tells the Apostles.
14-16. In Sacred Scripture "world" has a number of meanings. First, it means the whole of creation (Gen 1:1ff) and, within creation, mankind, which God loves most tenderly (Prov 8:31). This is the meaning intended here when our Lord says, "I do not pray that thou shouldst take them out of the world, but that thou shouldst keep them from the evil one" (v. 15). "I have taught this constantly using words from holy Scripture. The world is not evil, because it has come from God's hands, because it is his creation, because Yahweh looked upon it and saw that it was good (cf. Gen 1:7ff). We ourselves, mankind, make it evil and ugly with our sins and infidelities. Have no doubt: any kind of evasion from the honest realities of daily life is for you, men and women of the world, something opposed to the will of God" ([St] J. Escriva, "Conversations", 114).
In the second place, "world" refers to the things of this world, which do not last and which can be at odds with the things of the spirit (cf. Mt 16:26).
Finally, because evil men have been enslaved by sin and by the devil, "the ruler of the world" (Jn 12:31; 16:11), the "world" sometimes means God's enemy, something opposed to Christ and his followers (Jn 1:10). In this sense the "world" is evil, and therefore Jesus is not of the world, nor are his disciples (v. 16). It is also this pejorative meaning which is used by traditional teaching which describes the world, the flesh and the devil as enemies of the soul against which one has to be forever vigilant. "The world, the flesh and the devil are a band of adventurers who take advantage of the weakness of that savage you bear within you, and want you to hand over to them, in exchange for the glittering tinsel of a pleasure--which is worth nothing--the pure gold and the pearls and the diamonds and rubies drenched in the life-blood of your God-Redeemer, which are the price and the treasure of your eternity" ([St] J. Escriva, "The Way", 708).
17-19. Jesus prays for the holiness of his disciples. God alone is the Holy One; in his holiness people and things share. "Sanctifying" has to do with consecrating and dedicating something to God, excluding it from being used for profane purposes; thus God says to Jeremiah: "Before I formed you in the womb I knew you, and before you were born I consecrated you; I appointed you a prophet to the nations" (Jer 1:5). If something is to be consecrated to God it must be perfect, that is, holy. Hence, a consecrated person needs to have moral sanctity, needs to be practising the moral virtues. Our Lord here asks for both things for his disciples, because they need them if they are to fulfill their supernatural mission in the world.
"For their sake I consecrate myself": these words mean that Jesus Christ, who has been burdened with the sins of men, consecrates himself to the Father through his sacrifice on the Cross. By this are all Christians sanctified: "So Jesus also suffered outside the gate in order to sanctify the people through his own blood" (Heb 13:12). So, after Christ's death, men have been made sons of God by Baptism, sharers in the divine nature and enabled to attain the holiness to which they have been called (cf. Vatican II, "Lumen Gentium", 40).
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.