Jesus prayed, “Sanctify them in the truth. Your word is truth” (John 17:17). That prayer is not a mere wish but a certainty. Every request of the Son is perfectly aligned with the Father’s will, and every prayer of the Son is answered. He Himself declared, “Father, I thank You that You always hear Me” (John 11:42). His intercession is never denied, never delayed, never ineffective. When Jesus prays for His people, it is as good as done. If you are in Christ, your sanctification is not left hanging in the balance, dependent on your strength alone. It is secured by the perfect petition of the perfect High Priest. Holiness, then, is not an optional add-on. It is God’s unbreakable purpose for you, and He will bring it to completion.
The word sanctify comes from hagiazo, meaning to set apart, to consecrate, to make holy. In Scripture, ordinary things became holy when God set them aside for His service, such as the vessels in the temple. If that was true of bowls and lampstands, how much more is it true of blood-bought people. “You are not your own, for you were bought with a price” (1 Corinthians 6:19–20). Holiness is not mere rule-keeping. It is belonging to God for God, separation from sin and dedication to the Lord. Those vessels, once consecrated, could not be taken home by a priest for a private meal. They belonged exclusively to God’s house, set apart for His service, and to be used only when and how He commanded. That picture helps us grasp what it means to be sanctified: we are not common any longer, not available for just any use, but kept for the Lord.
The Bible speaks of sanctification in three tenses: past, present, and future. The first is positional sanctification. At conversion, God decisively sets us apart in Christ. This is a change of status and realm. Paul can tell a very messy church, “You were washed, you were sanctified, you were justified” (1 Corinthians 6:11). He even addresses them as “those sanctified in Christ Jesus, called to be saints” (1 Corinthians 1:2). Every Christian is a saint in this sense, not an elite few, but all who call upon the name of the Lord. This aspect is done, completed, and entirely God’s act. It gives us a new identity and standing before Him. And because it rests on Christ’s finished work, it cannot be undone. When shame whispers, “You are what you did,” positional sanctification answers, “No, I am who I am in Christ.”
The second aspect is progressive sanctification. This is the daily, lifelong work of the Spirit making us more like Jesus in thought, word, and deed. It is what Jesus prayed for in John 17:17. God uses a holy instrument, His holy Word, to produce holy people. Like produces like. “All Scripture is breathed out by God and profitable… for training in righteousness” so that we are “equipped for every good work” (2 Timothy 3:16–17). Teaching shows the path, reproof shows where we left it, correction brings us back, and training helps us stay on it. Growth is not a straight line upward but often three steps forward, two steps back. Bear in mind, struggle with sin is itself evidence of life, for before conversion we made peace with sin, but after conversion we make war. Yet we must be clear: in this world we never quite reach perfection in holiness. Progressive sanctification is real and observable, but it is always partial until the day of glorification.
And here is the certainty: the Spirit never abandons His work. Paul prayed, “May the God of peace Himself sanctify you completely” (1 Thessalonians 5:23), and then immediately added, “He who calls you is faithful; He will surely do it” (v. 24). The God who began the good work will not leave it half-finished. As Paul writes in Philippians 1:6, “He who began a good work in you will bring it to completion at the day of Jesus Christ.” He takes personal responsibility for your growth in holiness. Theologians have described this beautifully. Berkhof called it “a gracious, continuous work that delivers from the pollution of sin, renews the whole nature, and enables good works.” Hodge said sanctification is both definitive and progressive: a decisive break with sin at conversion and an ongoing renewal. Calvin insisted that Christ justifies no one whom He does not also sanctify. Justification and sanctification are distinct but never divided. The Spirit works through the Word, prayer, the ordinances, and the fellowship of the church. Growth in holiness is a community project, not a solo endeavor, and it is guaranteed by the faithful hand of God.
The third aspect is perfected sanctification. One day the process will be complete. We will be presented “without spot or wrinkle” (Ephesians 5:27). “He will establish your hearts blameless in holiness” at the coming of Christ (1 Thessalonians 3:13). This is glorification, when there will be no more sin and no more inward war, only full conformity to Christ. For the believer who dies before Christ returns, glorification occurs at death, when the soul is made perfectly holy and enters the immediate presence of the Lord. For those alive at His return, glorification will happen in a moment, as our bodies are transformed and we are caught up to be with Him forever (1 Corinthians 15:51–53; 1 Thessalonians 4:16–17). So certain it is that glorification will occur for the true child of God, Paul writes of it in the past tense: “those whom He justified He also glorified” (Romans 8:30). In other words, it is as good as done. Every struggling saint will be glorified. Nothing can derail God’s purpose—not Satan, not the world, not even the weakness of our own flesh. We aim at holiness now with all our might, but we rest in the assurance that God Himself will finish the work.
These truths protect us from confusion. Sanctification is not the basis of salvation. We are saved by grace alone, through faith alone, in Christ alone. Yet it is not optional, for “without holiness no one will see the Lord” (Hebrews 12:14). Fruit does not save, but living trees bear fruit. It is also not passive. The Christian life is not “let go and let God.” Scripture calls us to “work out” what God “works in” (Philippians 2:12–13). We strive, but God supplies. We labor, but God empowers. And because His power undergirds our striving, the outcome is never in doubt.
Think of a surgeon’s scalpel, sterilized and placed in skilled hands. By itself, it does nothing. In the surgeon’s hands, it becomes an instrument of healing. The Spirit is the divine Surgeon. The Word is His pure instrument. The Spirit takes the Word and cuts away what does not belong, not to harm but to heal, until the likeness of Christ emerges more clearly.
Holiness requires balance. Some fall into legalism, defining holiness only by what they do not do. Others abuse grace as a license to ignore God’s commands. True holiness is both putting off the old and putting on the new. It is separation from sin and consecration to God. It is not isolation either. We grow together in the church through worship, preaching, fellowship, and discipline. Nor is it despair. Positional sanctification reminds us that we are already set apart. Progressive sanctification assures us that God is presently at work within us. Perfected sanctification guarantees that one day we will be made complete. In every stage, certainty rests not on us but on Christ.
What does growth look like in practice? It means daily intake of the Word, praying that the Spirit would make it fruitful. It means continual repentance, keeping short accounts with God. It means walking in fellowship with the church and making use of the means of grace. It means guarding our inputs, since what we behold shapes what we become. And it means serving others, for holiness grows as we give ourselves away. As Luther put it, “God doesn’t need your good works. Your neighbor does.”
At the heart of it all is Christ. Sanctification begins, continues, and ends with Him. He is the One who sets us apart, the One who by His Word and Spirit is making us new, and the One who will present us faultless with great joy. The gospel not only pardons, it purifies. The grace that declares us righteous begins to make us righteous until the day when faith becomes sight. We have been sanctified in Christ. We are being sanctified by the Spirit through the Word. And we will be sanctified completely at His coming. And because Jesus prayed for it, it is certain.