Some persons take the high priestly prayer of Jesus at John 17 to contain some powerful evidences in favor of an Augustinian-Reformed view of God's salvific intentions and purposes. On this view of things, God does not intend to save all persons but only some, and it is precisely for these persons that Christ accomplishes atonement for sin. Hence the doctrine of limited or definite atonement. I don't agree with this scheme of things, and I happen to think the high priestly prayer contains the opposite message.
Jesus opens his prayer with the affirmation that he has received authority over all persons: Father, the hour has come; glorify your Son so that the Son may glorify you, since you have given him authority over all people, to give eternal life to all whom you have given him (17.1-2). This is, to my mind, a very powerful and unambiguous statement of God's universal salvific intentions: the Son receives authority over all, so that he may give life to all those given him. I don't see why there should be any distinction supposed between those whom the Father has given the Son, and those over whom the Father has given the Son authority. What is it to belong to the Son, if not that the Son has authority over you?
Some objectors may note that Jesus later makes a distinction between the world and those whom the Father has given him from the world (v. 6). This, the suggestion goes, shows that it is not all one to be given to the Son, and to be given under the authority of the Son. But this point is not at all obvious. In the first place, it is evident that the phrase "those whom you have given me" from v. 6 onward refers not to "the elect" as the Augustinian-Reformed understands the phrase, but to the apostles. This is evident because he later goes on to pray not only on behalf of these, but also on behalf of those who will believe in me through their word (v. 20). Moreover he says that they now, at the time of his prayer, know that everything Jesus has received is from the Father, and that Jesus has given them the words he received from the Father (vv. 7-8). These things clearly could not have been said of future believers who were not even born at that moment, let alone of those who would believe but had not yet come into contact with the gospel. It is evident, then, that the phrase those whom you have given me at v. 6 is a special reference to the apostles. It would be absurd to suppose that we could identify the scope of this usage with the usage of those whom you have given him in v. 2, as if Jesus only gives eternal life to the apostles.
Importantly, however, Jesus does not lose sight even of the world. He goes on to pray for those who would believe through the testimony of the apostles that they may all be one. As you, Father, are in me and I am in you, may they also be in us, so that the world may believe that you have sent me (v. 21). Jesus prayers for the unity of believers so that the world may learn and come to believe that he has been sent of the Father. This is the question that had been debated over the course of twelve or so chapters in John's gospel: where does Jesus come from? By whose authority does he do the things we've seen? What is his relation to God -- is he a sinner or the promised Christ? To believe that he has come from God is the definition of salvation for John's gospel, and the one who believes that Jesus is the Son of God, the Christ of God, the Holy One of God, etc., is to have eternal life. Jesus consequently prays for the salvation of the world as well.
We must not forget, either, that there are numerous affirmations in John's gospel that God's salvific intentions are universal, encompassing the whole creation. The Samaritans come to believe that Jesus is the Savior of the world (4.42), which phrase echoes John's words in his epistle: we have seen and testify that the Father sent his Son as the Savior of the world (1 John 4.14). Jesus says in the bread-of-life discourse that he gives his flesh for the life of the world (John 6.51). He says further that he will drag all persons to himself upon being lifted up (12.32).
For these reasons I think the high priestly prayer does not support a doctrine of definite atonement. Rather the universalist affirmation of vv. 1-2 remains, and the remainder of the prayer is concerned with the salvation of a slowly expanding group: first he prays for the apostles; then he prays for later believers, as well as for the whole world. He begins his prayer with an affirmation of God's universal salvific purposes, and this cannot be lost.