While cyber sex (sexting or online pornography) did not exist in biblical times, the Bible is clear regarding the principles involved. Jesus personally noted that God provided a particular design for family and human sexuality that His people are to follow.
Is it a sin to engage in cyber sex / phone sex?
Humans were designed in God's image to live within a marriage relationship between one man and one woman in which sexual activity strengthens the relationship and has the potential to build one's family through children. God specifically noted man and woman are both created in His image: "So God created man in his own image, in the image of God he created him; male and female he created them" (Genesis 1:27).
When a man and woman come together in marriage, God noted, "Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh" (Genesis 2:24). Jesus commented on this very verse, teaching, "So they are no longer two but one flesh. What therefore God has joined together, let not man separate" (Matthew 19:6).
Variations from this God-designed ideal result in a variety of personal, family, and society concerns. In particular, the New Testament teaches believers to avoid lust and adultery, addressing both the desire and actions involved in sexual immorality (Matthew 5:27-28).
Cyber sex may not include literal, physical sex, yet does involve sexual thoughts, desires, and actions that displease God and are condemned as sinful in Scripture. Instead, God encourages, "Finally, brothers, whatever is true, whatever is honorable, whatever is just, whatever is pure, whatever is lovely, whatever is commendable, if there is any excellence, if there is anything worthy of praise, think about these things" (Philippians 4:8).
Further, Hebrews 13:4 teaches, "Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous." An "undefiled" marriage here includes both avoiding adultery and other forms of sexual immorality. This could include any other forms of lust, pornography, sexual fantasies, and cyber sex. The believer in Christ should instead seek to honor God through thoughts and actions that please the Lord, help others, and support godly families.
Finally, it should be noted that various sexual addictions are an area of weakness for some people. Those who struggle in this particular area should not be viewed as "worse sinners" or beyond help. Instead, those who struggle should be encouraged to seek help, hope, and accountability with a trusted friend, counselor, or other person who can help improve spiritual growth in this area.
What does the Bible say about lust? What is lust?
Is pornography a sin?
What practical steps can I take to overcome an addiction to internet porn?
Is masturbation a sin according to the Bible?
Is it a sin to have intrusive thoughts?
Truth about Sin