Charles Spurgeon said, " Christ will be master of the heart, and sin must be mortified. If your life is unholy, then your heart is unchanged, and you are an unsaved person. The Savior will sanctify His people, renew them, give them a hatred of sin, and a love of holiness. The grace that does not make a man better than others is a worthless counterfeit. Christ saves His people, not IN their sins, but FROM their sins. Without holiness, no man shall see the Lord."
The Apostle Paul said to the Thessalonians, "For this is the will of God, your sanctification : that you should abstain from sexual immorality" (4:3). Sanctification means "to be set apart." It is a setting apart from sin to Christ. The Thessalonians had already "turned to God from idols" (1:9) but now they needed to "know how to possess (their) own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God" (4:4-5). As Spurgeon has well noted "If your life is unholy, then your heart is unchanged, and you are an unsaved person." Are you living your life "set apart" to Christ? Are you abstaining from porneia (sexual immorality)? Are you pleasing God in your walk with Him? "For God did not call us to uncleanness, but in holiness" (4:7).