We who are true believers are valuable to God, and our relationship with God is valuable to Him. If this were not so He would not have sent His Son to die for us. God redeemed us for Himself so that we can enjoy fellowship with him forever.
Therefore, since our relationship with God is so important, we must be careful not to do and experience things that God hates. We must take special care not to commit sexual immorality, for our bodies and mind belong to Christ. Sex is an extremely intimate act between two people. It brings glory to God when it is done in a holy, God-honoring way, but it brings disgrace when it is engaged in a selfish, sinful way. When we have sex with a person we shouldn’t have sex with we are saying that the physical attraction of their body is more important to us than our relationship with God. We should not covet a relationship with another person, which by very nature contradicts our relationship with God:
Do you not know that your bodies are members of Christ himself? Shall I then take the members of Christ and unite them with a prostitute? Never! 16 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.” 17 But whoever is united with the Lord is one with him in spirit. (I Corinthians 6:15-17 NIV)
Sex is an act of unity. It is good for a man to unite in this way with his wife to whom he has pledged a lifetime of exclusive loyalty. But it is not good for him to unite with someone who is pledged to someone else. This breach of trust, this sin, is dishonorable to both parties involved. If a Christian does this, it dishonors the Lord who “is one with him in spirit.”
Therefore, we as Christians need to flee sexual immorality. This means we need to not only avoid the actual act, but, as Jesus said, we even need to fight against immoral fantasies:
“You have heard that it was said, ‘You shall not commit adultery.’ 28 But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. (Matthew 5:27-28 NIV)
This is the problem with pornography: those who engage only in pornography might not be committing the physical act with another person, but they are still doing it spiritually in their mind. This dishonors God. Therefore, as Christians we need to pray to God for strength and constantly fight against sexual temptation, even against the fantasies in our mind. We need to not be passive targets for sin: in addition to fighting against bad thoughts, we need to aggressively fill our minds with good thoughts. This means we need to focus our attention and imagination on serving God, and if we are married, we need to focus our attention and imagination on serving our spouse’s spiritual and sexual needs. We need to humbly ask God for help to fight against sexual temptations that would bring dishonor to the name of Christ.