Now in putting up a title like that, it may appear that I am being legalistic and judgemental. From the outset I should state that we are saved by the Grace of God alone. That is, God has sent his son to suffer the judgement that we deserve so that we can come into a relationship with him. The views presented here are only relevant for Christians, for those who have responded to what God has already done for them in Christ.
Marriage is a very special thing in the eyes of God, a marvellous gift from God to human beings. The first and most crucial bible passage about marriage is Genesis 2:24, which speaks of the creation of marriage.
"For this reason a man shall leave his father and his mother, and be joined to his wife; and they shall become one flesh."
In the New testament, both Jesus and Paul apply this text to marriage. Jesus cites it to explain why he abhors divorce so much. Paul goes further and tells us what marriage is really about, why God created it. In rich and beautiful language, Paul explains that marriage is really all about Christ and the Church. The husband is called to show the kind of sacrificial love towards his wife that Christ did towards the Church in redeeming her and the wife is called to submit to this as the Church submits to Christ out of love, trusting in him. So marriage is a beautiful, gospel proclaiming thing.
However, in speaking of prostitution, Paul quotes exactly the same passage:
"Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, "The two will become one flesh." "
(1 Corinthians 6:16)
So this foundational passage about marriage is also about sex. In the biblical worldview, the two belong together. This is why in the same letter, Paul urges married couples not to abstain from sex (1 Corinthians 7:5) and also urges the unmarried to marry if they cannot keep themselves under control (1 Corinthians 7:8-9). For Paul, sex and marriage should not be separated. Marriage is the answer to the problem of sexual immorality.