I pray for them: I pray not for the world, but for them which Thou hast given Me; for they are Thine…Sanctify them through Thy truth: Thy word is truth. – John 17:9,17

I want you to notice for whom this prayer was offered. It was not offered for the world outside. It would not be a suitable prayer for those who are dead in sin. Our Lord referred to the company of men and women who were already saved, of whom He said that they had kept God’s Word: “Thine they were, and Thou gavest them Me.” They were therefore sanctified already in the sense of being consecrated and set apart for holy purposes; and they were also sanctified in a measure already in the sense of being made holy in character; for the immediate disciples of our Lord, with all their errors and deficiencies, were holy men. It was for the apostles that Jesus thus prayed; so that we may be sure that the most eminent saints need still to have this prayer offered for them: “Sanctify them through Thy truth.” Though, my sisters, you may be Deborahs, worthy to be called mothers in Israel, yet you need to be made more holy. Though, my brethren, you may be true fathers in God, of whom the Scripture saith truly that we have “not many,” yet you still need that Jesus should pray for you: “Sanctify them through Thy truth.”

Those who are most pure and honorable have yet their shortcomings and errors to mourn over. When the Lord turns the light strong upon us, we soon see the spots upon our raiment; it is indeed when we walk in the light as God is in the light that we see most our need of the cleansing blood of Jesus. If we have done well, to God be the glory of it; but we might have done better. If we have loved much, to God’s grace be the praise; but we ought to have loved more. If we have believed, and believed steadfastly, we ought to have believed to a far higher degree in our Almighty Friend. We are still below our capacities; there is a something yet beyond us. O ye sanctified ones, it is for you that Jesus prays that the Father may still sanctify you. “Neither pray I for these alone, but for them also which shall believe on Me through their word…” – John 17:20 ~ C.H. Spurgeon

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