It makes us think about time from God's standpoint. If we were, we would not need the ransom. Nonetheless we are to strive to be free from sin and fleshly desires. We should seek to be both physically pure and mentally pure. Although harder to obtain, mental purity is the key to building a Christ-like character.
Physical purity involves keeping the body pure.
Every other sin that a man commits is outside the body, but the immoral man sins against his own body. In verse 18, Paul specifically addresses sexual purity. Yet it is a key principle and a type of the virgin bride of Christ. We canbe examples of purity to those in the world by clearly making known our decisions on this subject. Mental purity involves keeping one's mind from all evil and sinful thoughts so that one may focus more on God.