How can I know what is a sin and what isn't?The Bible is clear on a great many sins. Proverbs 6:16-19 mentions pride, lying, and murder, among others. Galatians 5:19-21 adds sexual immorality, idolatry, witchcraft, hatred, and jealousy. And 1 Corinthians 6:9-10 includes stealing, swindling, and drunkenness. But there are many more circumstances that are not as clear. Part of maturing as a Christian is recognizing that the freedom we receive in Christ comes with a responsibility to live as Christ. We are not children to be given a list of do's and don'ts and gold stars and check marks. We are adults, or we are to become adults (Hebrews 5:11-14), who live in Christ, motivated by love for God and others.
Romans 14 is a key passage on this subject. It starts by saying that outside of the basics, people will have different opinions about right and wrong, and neither side should judge the other. God has placed each individual in specific circumstances which may endorse different standards. There are tribes in South America where shirtless women are not considered nude. But a woman who displays her armpits is because she is exposing hair that developed during puberty. Women in that culture keep their arms down while others of us would require a shirt, but both actions are expressions of godly modesty. Verse 4 explains we are judged by God, and should be gentle with each other.
A sure sign that something is a sin is if it is not personally edifying. In 1 Corinthians 6:12, Paul says, "Everything is permissible for me—but not everything is beneficial. Everything is permissible for me—but I will not be mastered by anything." He would not be "mastered"—that is, he would not allow a gray area to become more important than his relationship with God. John Wesley's mother put it this way: "Whatever weakens your reasoning, impairs the tenderness of your conscience, obscures your sense of God, or takes away your relish for spiritual things, in short if anything increases the authority and the power of the flesh over the spirit, that to you becomes sin, however good it is in itself."
In Romans 14, Paul details how our actions may affect others. Verse 15: "If your brother or sister is distressed because of what you eat, you are no longer acting in love. Do not by your eating destroy someone for whom Christ died." In all things, not just eating, we should consider what will edify those around us. We should not destroy the work of God for trivialities (vs. 20), but value others more than our own desires (Romans 15:1).
Verse 8 states, "If we live, we live for the Lord; and if we die, we die for the Lord. So, whether we live or die, we belong to the Lord." Living to the Lord means obeying His commandments to love Him and love others. We are to live our lives in a constant state of love, and that is what determines our actions when the road is less clear. Everything we do should be driven by faith (vs. 23)—conviction or firm persuasion. If we are not completely convicted about the act itself, we should be governed by something we are convicted of—God wants us to love Him and love others. If the act in question does not meet those criteria, it should not be done.
Does the Bible have a list of sins?
What are the seven deadly sins?
Are all sins equal?
Does my private, personal sin affect others?
The consequences of sin - What are they?
Truth about Sin