John 17:17

17. Sanctify them In the three ensuing verses Jesus represents their consecration to their mission. God must sanctify them as Christ sanctifies himself. To sanctify is to set apart to some special divine use; and this may or may not require an inner purification of the being set apart. If an unholy being, as man, be set apart to a pure use, he must be rendered internally as pure as the use to which he is appropriated. Of an indifferent thing, neither intrinsically holy or unholy, as a vessel for the sanctuary service, there can be no purification but a physical one with an emblematical meaning. Where a holy being, as Christ, is set apart for a holy work, as for the work of redemption, no inward purification is possible; for he is already perfectly pure. It is a consecration of the holy to the holy. The use to which man is divinely consecrated is eternal service in the sanctuary of heaven; but to attain this use his entire purification must be perfect. If he fails in this his failure is total.

Through thy truth Rather in thy truth.

Thy word is truth Thy word doubtless means the Gospel revelation, both in its doctrinal and preceptive parts; its doctrinal parts exhibiting the scheme of salvation, its preceptive enjoining us to obey its conditions. The agent of this sanctification through or in the Gospel, according to Jesus’s prayer is God, who both gives the Gospel which sanctifies, and animates it by his Spirit to a sanctifying power. Hence it is not the mere instrumental truth, it is the divine Spirit, which sanctifies.