The Bible tells us to run away from every appearance of evil. We should avoid evil at all costs. We know that sin is evil. We should stay away from sin. We should follow after righteousness and righteous courses. We are christians who have turned away from sin. So, we should not continue in sin. Sin is breaking God's standard.
The christian life demands discipline. We must learn to practice discipline. We should not allow our lustful desires to have the upper hand over us. We should trust in God and obey His commandments. There are many things which other people do not consider important which we as christians must take note of. We should not live our lives carelessly as other people in the society live.
In the church, members are not permitted to have sexual relationships when they are not married. It is a sin if anyone does that. That is fornication. When two people of opposite sex, who are not married, have intercourse together, it is a sin. We should avoid that as followers of Jesus Christ.