Definition and Nature:
Sanctification, in Christian theology, refers to the process of being made holy, set apart for God's purposes, and conformed to the image of Christ. It is both an instantaneous act and a progressive work of God in the life of a believer. Through Christ, sanctification is initiated, sustained, and ultimately completed.

Biblical Foundation:
The New Testament provides a robust framework for understanding sanctification through Christ. In 1 Corinthians 1:30, the Apostle Paul writes, "It is because of Him that you are in Christ Jesus, who has become for us wisdom from God: our righteousness, holiness, and redemption." Here, Christ is identified as the source of holiness, indicating that sanctification is rooted in the believer's union with Him.

Positional Sanctification:
Upon conversion, believers are positionally sanctified, meaning they are declared holy and set apart for God. This is a definitive act accomplished by Christ's sacrifice. Hebrews 10:10 states, "And by that will, we have been sanctified through the sacrifice of the body of Jesus Christ once for all." This verse underscores the completed work of Christ on the cross, which secures the believer's sanctified status before God.

Progressive Sanctification:
While positional sanctification is immediate, progressive sanctification is an ongoing process. It involves the believer's growth in holiness and conformity to the character of Christ. Philippians 2:12-13 exhorts believers to "work out your salvation with fear and trembling, for it is God who works in you to will and to act on behalf of His good purpose." This passage highlights the cooperative nature of sanctification, where the believer actively participates in the process, empowered by God's Spirit.

Role of the Holy Spirit:
The Holy Spirit plays a crucial role in sanctification, guiding, teaching, and transforming believers. In 2 Thessalonians 2:13, Paul writes, "But we should always thank God for you, brothers and sisters 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 Spirit's work is essential in applying the redemptive work of Christ to the believer's life, enabling them to live in obedience to God's will.

Means of Sanctification:
Sanctification is facilitated through various means, including the Word of God, prayer, and the sacraments. Jesus prayed for His disciples in John 17:17, saying, "Sanctify them by the truth; Your word is truth." The Scriptures serve as a primary tool for sanctification, providing instruction, correction, and encouragement. Additionally, prayer and participation in the sacraments, such as baptism and the Lord's Supper, are vital practices that nurture spiritual growth and holiness.

Ultimate Sanctification:
The process of sanctification will be completed at the return of Christ, when believers are fully conformed to His image. 1 John 3:2 offers this hope: "Beloved, we are now children of God, and what we will be has not yet been revealed. We know that when Christ appears, we will be like Him, for we will see Him as He is." This future aspect of sanctification assures believers of their ultimate transformation and glorification.

Conclusion:
Sanctification through Christ is a comprehensive work that encompasses the believer's past, present, and future. It is initiated by Christ's atoning sacrifice, sustained by the Holy Spirit, and completed at His return. Through this divine process, believers are progressively conformed to the likeness of Christ, reflecting His holiness in their lives.