Definition and Overview:
Sanctification by faith is a theological concept that refers to the process by which believers in Jesus Christ are made holy through faith. It is an integral part of the Christian doctrine of salvation, emphasizing that sanctification is not achieved by human effort alone but through the work of the Holy Spirit in conjunction with the believer's faith in Christ. This process involves being set apart for God's purposes and growing in spiritual maturity and holiness.

Biblical Foundation:
The concept of sanctification by faith is rooted in several key passages of Scripture. In the New Testament, the Apostle Paul frequently addresses the role of faith in the believer's sanctification. In Acts 26:18, Paul recounts his commission from Christ, stating, "to open their eyes, so that they may turn from darkness to light and from the power of Satan to God, that they may receive forgiveness of sins and an inheritance among those sanctified by faith in Me."

Paul further elaborates on this in his epistles. In Romans 5:1-2, he writes, "Therefore, since we have been justified through faith, we have peace with God through our Lord Jesus Christ, through whom we have gained access by faith into this grace in which we stand. And we rejoice in the hope of the glory of God." Here, Paul connects justification and sanctification, both accessed through faith.

The Role of the Holy Spirit:
Sanctification by faith is deeply connected to the work of the Holy Spirit. In 2 Thessalonians 2:13, Paul states, "But we should always thank God for you, brothers who are loved by the Lord, because God has chosen you from the beginning to be saved by the sanctification of the Spirit and by faith in the truth." The Holy Spirit is the agent of sanctification, working within believers to transform them into the likeness of Christ.

Faith and Works:
While sanctification is by faith, it naturally results in good works. James 2:26 reminds believers that "faith without deeds is dead." Genuine faith produces a life characterized by obedience and good works, which are the fruit of sanctification. Ephesians 2:10 affirms this, stating, "For we are God's workmanship, created in Christ Jesus to do good works, which God prepared in advance for us to do."

Progressive Nature:
Sanctification is both a definitive act and a progressive process. Hebrews 10:14 declares, "For by a single offering He has perfected for all time those who are being sanctified." This verse highlights the already-but-not-yet aspect of sanctification: believers are positionally sanctified in Christ but are also being progressively sanctified in their daily lives.

Faith's Role in the Believer's Life:
Faith is the means by which believers access the grace necessary for sanctification. Galatians 2:20 illustrates this dynamic: "I have been crucified with Christ, and I no longer live, but Christ lives in me. The life I live in the body, I live by faith in the Son of God, who loved me and gave Himself up for me." This faith is not passive but active, continually trusting in Christ's finished work and the Spirit's ongoing work.

Conclusion:
Sanctification by faith is a vital doctrine that underscores the believer's dependence on God's grace and the Holy Spirit's power to grow in holiness. It is a transformative process that begins at conversion and continues throughout the believer's life, culminating in ultimate glorification with Christ.