For this is the will of God, your sanctification; that is, that you abstain from sexual immorality…
Sanctification is a large word both linguistically and theologically. Linguistically, the word sanctification comes from the term “to sanctify,” or “to set apart.” Theologically, the term points to you, the Christian, and your lifelong duty to continually mature in your relationship with Christ. The process of sanctification, as it is called, is simply looking more like Christ today than you did yesterday.
The fourth chapter of Paul’s first letter to the church in Thessalonica addresses this process. “Finally then, brethren, we request and exhort you in the Lord Jesus, that, as you received from us instruction as to how you ought to walk and please God (just as you actually do walk), that you may excel more (4:1). Paul acknowledged that the Thessalonians were indeed walking to please God (as you too might be). Nonetheless, he encouraged them still to “excel more.” The Thessalonians struggled with sexual immorality, so Paul addresses the sin. “For this is the will of God, your sanctification; that is, that you abstain from sexual immorality…”
I do not know what type of sin you are struggling with the most today. It doesn’t really matter though. The point of this verse is your sanctification. You, your parents, and every other Christian need will need further sanctification every day from now until the day they die. This is one of but a few passages in Scripture where “God’s will” is spelled out so clearly. I pray that you make it your goal to look more like Christ tomorrow than you did today.