Matthew Henry 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)

Christ next prayed for the disciples, that they might not only be kept from evil, but be made good. It is the prayer of Jesus for all who are his, that they may be made holy. Even disciples must pray for sanctifying grace.

The means of giving this grace is, through your truth, your word is truth. Sanctify them, set them apart for yourself and your service. Acknowledge them in their office; let your hand go with them.

Jesus entirely devoted himself to his undertaking and all its parts, especially the offering up himself without spot to God, by the eternal Spirit. The real holiness of all true Christians is the fruit of Christ's death, by which the gift of the Holy Ghost was purchased; he gave himself for his church, to sanctify it. If our views do not have this effect on us, they are not Divine truth, or we do not receive them by a living and a working faith, but as mere notions.