New Defender's Study Bible Notes
4:3 sanctification. “Sanctification” (Greek hagiasmos) is used to indicate both separation to God (I Corinthians 1:30; II Thessalonians 2:13; I Peter 1:2) and the holy lifestyle of those so separated (I Thessalonians 4:4,7; Romans 6:19,22; I Timothy 2:15; Hebrews 12:14). When Christians are seeking to find the will of God for their lives, they should recognize that His will centers, first of all, on their sanctification—that is, the total dedication of their lives, as redeemed sinners, to Christ.
4:3 abstain from fornication. While there may be questions about engaging in “doubtful” things (Romans 14:1), there can be no doubt at all—even in this permissive age—that fornication (that is, any sexual relationship outside of heterosexual marriage) is always contrary to God’s will. Engaging in it will inevitably bring grief.