Why is sexual purity so important?

God gave man and woman the joy and pleasure of sexual relations within
the bounds of marriage, and the Bible is clear about the importance of
maintaining sexual purity within the boundaries of that union between
man and wife (Ephesians 5:31). Humans are well aware of the pleasing
effect of this gift from God but have expanded it well beyond marriage
and into virtually any circumstance. The secular world's philosophy of
"if it feels good, do it" pervades cultures, especially in the West,
to the point where sexual purity is seen as archaic and unnecessary.

Yet look at what God says about sexual purity. "You should be
sanctified: that you should avoid sexual immorality; that each of you
should learn to control his own body in a way that is holy and
honorable, not in passionate lust like the heathen, who do not know
God. . . . For God did not call us to be impure, but to live a holy
life" (1 Thessalonians 4:3–5, 7). This passage outlines God's reasons
for calling for sexual purity in the lives of His children.

First, we are "sanctified," and for that reason we are to avoid sexual
immorality. The Greek word translated "sanctified" means literally
"purified, made holy, consecrated [unto God]." As Christians, we are
to live a purified life because we have been made holy by the exchange
of our sin for the righteousness of Christ on the cross and have been
made completely new creations in Christ (2 Corinthians 5:17–21). Our
old natures, with all their impurities, sexual and otherwise, have
died, and now the life we live, we live by faith in the One who died
for us (Galatians 2:20). To continue in sexual impurity (fornication)
is to deny that, and doing so is, in fact, a legitimate reason to
question whether we have ever truly been born again. Sanctification,
the process by which we become more and more Christlike, is an
essential evidence of the reality of our salvation.

We also see in 1 Thessalonians 4:3–5 the necessity of controlling our
bodies. When we give in to sexual immorality, we give evidence that
the Holy Spirit is not filling us because we do not possess one of the
fruits of the Spirit—self-control. All believers display the fruit of
the Spirit (Galatians 5:22–23) to a greater or lesser degree depending
on whether or not we are allowing the Spirit to have control.
Uncontrolled "passionate lust" is a work of the flesh (Galatians
5:19), not of the Spirit. So controlling our lusts and living sexually
pure lives is essential to anyone who professes to know Christ. In
doing so, we honor God with our bodies (1 Corinthians 6:18–20).

We know God's rules and discipline reflect His love for us. Following
what He says can only help us during our time on earth. By maintaining
sexual purity before marriage, we avoid emotional entanglements that
may negatively affect future relationships and marriages. Further, by
keeping the marriage bed pure (Hebrews 13:4), we can experience
unreserved love for our mates, which is surpassed only by God's
enormous love for us.