“Sanctify them through thy truth: thy word is truth” (John 17:17).
Jesus Christ prayed to His Heavenly Father for His followers in Israel’s program (especially His Apostles—John 17:12). He would do likewise for us today in the Dispensation of Grace.
Sanctification is not to be confused with justification. The former is to be “set apart for the purpose for which God intended;” the latter means “declared righteous before God.” One must be justified (righteousness imputed to his account) before he can be sanctified (useful to God’s work—“holy,” a “saint”).
Just moments before His arrest, Christ in the Garden of Gethsemane communes with Father God by praying throughout John chapter 17. Verse 8 is crucial to grasping today’s Scripture: “For I have given unto them the words which thou gavest me: and they have received them, and have known surely that I came out from thee, and they have believed that thou didst send me.” Now, verse 14: “I have given them thy word; and the world hath hated them, because they are not of the world, even as I am not of the world.”
The Lord was not praying for His followers to be saved unto eternal life (they were already justified). What He desired was spiritual fruit, their identity in Him being manifested in the form of works. Father God’s Word—which He (Jesus) had just taught them for over three years—would be how the Holy Father would use those men for His purposes. He would send His Holy Spirit (Acts chapter 2) to empower them according to the words He had already given them in Christ’s earthly ministry. That message would be further expanded once the Holy Spirit came (see John 14:26; John 15:25-27; John 16:7-14).
“For this cause also thank we God without ceasing, because, when ye received the word of God which ye heard of us, ye received it not as the word of men, but as it is in truth, the word of God, which effectually worketh also in you that believe” (1 Thessalonians 2:13). Saints, God’s Word to us—Paul’s epistles, Romans through Philemon—will effectually work in us on a daily basis if we believe it. Then, we too will be “sanctified through [God’s] truth!” source