Sanctify them by Your truth. Your Word is truth…And for their sakes I sanctify Myself, that they also may be sanctified by the truth. – John 17:17, 19

This chapter, which ought to be universally known as the Lord’s Prayer, may be called the holy of holies of the word of God. Here we are admitted to that secret place where the Son of God speaks with the Father in closest fellowship of love. Here we look into the heart of Jesus, as He sets out in order His desires and requests before His Father on our behalf. Here inspiration lifts her veil, and we behold truth face to face. Our text lies somewhere near the middle of the prayer; it is the heart of it. Our Lord’s desire for the sanctification of His people pervades the whole prayer; but it is gathered up, declared, and intensified in the one sentence: “Sanctify them through Thy truth: Thy Word is truth.” How invaluable must the blessing of sanctification be when our Lord, in the highest reach of His intercession, cries: “Sanctify them!” In sight of His passion, on the night before His death, our Savior lifts His eyes to the great Father, and cries in His most plaintive tones, “Father, sanctify them.” He asks this sanctification of God the Father Himself, for He alone it is who can sanctify His people. The place whereon we stand is holy ground, and the subject whereof we speak demands our solemn thought. Come, Holy Spirit, and teach us the full meaning of this prayer for holiness!

“For their sakes I sanctify Myself.” Our Lord’s sanctification was His consecration to the fulfillment of the Divine purpose; His absorption in the will of the Father. “Lo, I come to do Thy will, O God.” In this sense our interceding Lord asks that all His people may, by the Father, be ordained and consecrated unto holy service. The prayer means, “Father, consecrate them to Thine own self; let them be temples for Thine indwelling, instruments for Thy use.” He would have each of us consecrated unto the Lord, designated and ordained for divine purposes. We are not the world’s, else might we be ambitious; we are not Satan’s, else might we be covetous; we are not our own, else might we be selfish. We are bought with a price, and hence we are His by whom the price is paid. We belong to Jesus, and He presents us to His Father, and begs Him to accept us and sanctify us to His own purposes. Do we not most heartily concur in this dedication? Do we not cry, “Father, sanctify us to Thy service?” I am sure we do if we have realized our redeemed condition. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/1890.cfm