Thomas Aquinas Commentary John 17:17-19

"Sanctify them in the truth: thy word is truth. As thou didst send me into the world, even so sent I them into the world. And for their sakes I sanctify myself, that they themselves also may be sanctified in truth." — John 17:17-19 (ASV)

Previously, our Lord prayed for the protection of his disciples; here he prays for their sanctification.

1. He asks for their sanctification.
2. He mentions why they need to be sanctified: as you have sent me into the world.
3. He says this sanctification has already begun: and for them I do sanctify myself.

He says: I have prayed that my disciples be kept from evil, but this is not enough unless they are perfected by what is good: depart from evil, and do good (Psalms 37:27). Accordingly, he prays, Father, sanctify them, that is, perfect them and make them holy. And do this in the truth; that is, in me, your Son, who am the truth (John 14:6). It is like saying: make them share in my perfection and holiness. And so he adds, your word, that is, your Word, is truth. The meaning is then: sanctify them in me, the truth, because I, your Word, am the truth.

Or, we could say this: sanctify them by sending the Holy Spirit. And do this in truth, that is, in the knowledge of the truths of the faith and of your commandments: you will know the truth, and the truth will set you free (John 8:32). For we are sanctified by faith and the knowledge of the truth: the righteousness of God through faith in Jesus Christ for all who believe (Romans 3:22). He adds, your word is truth, because the truth of God’s words is unmixed with falsity: all the words of my mouth are righteous; there is nothing twisted or crooked in them (Proverbs 8:8). Furthermore, his word teaches the uncreated truth.

Another interpretation: in the Old Testament, everything set aside for divine worship was said to be sanctified: then bring near to you Aaron your brother, and his sons with him, from among the people of Israel to serve me as priests (Exodus 28:1). Accordingly, he says, sanctify them, that is, set them aside, in truth—that is, to preach your truth—because your word, which they are to preach, is truth.

The need for their sanctification is added when he says, as you have sent me into the world, I also have sent them into the world. He is saying in effect: I have come to preach the truth: for this I was born... that I should give testimony to the truth (John 18:37). And so I have sent my disciples to preach the truth: go into all the world and preach the Gospel to the whole creation (Mark 16:15). Accordingly, they have to be sanctified in the truth: as the Father has sent me, I also send you (John 20:21).

They need to be sanctified not only because of the task they have been given, but also because their sanctification has already been started by me. Thus, he says, and for them I do sanctify myself.

According to Augustine, we should note that there are two natures in Christ. Christ is holy by essence, considering his divine nature, while he is holy by grace, which is derived from the divine nature, considering his human nature. Referring to his divine nature, he says, I sanctify myself, by taking on flesh for them. I do this so that the sanctity or holiness of grace, which is in my humanity but is also from me as God, might flow from me to them, because of his fullness we all have received (John 1:16).

It is like the precious oil upon the head—and this head is Christ, who is God—running down upon the beard, upon the beard of Aaron—that is, upon his human nature—and from there, running down on the collar of his robes (Psalms 133:2), that is, to us.

Or, according to Chrysostom, he is asking that they be sanctified by a spiritual sanctification. In the Old Testament, there were sanctifications of the body: a cleansing of the body imposed until the time comes to set things right (Hebrews 9:10). These were figures of a spiritual sanctification, and these figures involved the offering of a sacrifice. And so it was appropriate that some sacrifice be offered for the sanctification of the disciples.

This is what he is saying: I sanctify myself so that they might be sanctified; that is, I am offering myself as a sacrifice: who offered himself without blemish to God (Hebrews 9:14); so Jesus also suffered outside the gate in order to sanctify the people through his own blood (Hebrews 13:12). He did this in truth, not in a figure, as was done in the Old Testament.