Thanks for your question. The Bible has different sections that outline what sin is. In the Old Testament, the 10 commandments were given to Moses at Mt Sinai that spelled out the essence of what it meant to follow God. Failure to follow the commandments was considered sin (e.g. Love God, honour your parents, do not murder etc). This was expanded on considerably in what is known as the ‘Law’ in the books of Leviticus & Deuteronomy. These were very detailed and included laws about sexual immorality, worshipping foreign gods and caring for the poor.
In the New Testament, there are various places where sins are catalogued. The Apostle Paul occasionally includes ‘vice’ lists in his letters such as this one from his letter to the church in Galatia
‘The acts of the sinful nature are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.’ (Galatians 5:19-21)
While these sins are broad ranging they are by no means exhaustive. When asked what was the greatest commandment Jesus replied: ‘Love the Lord your God with all your heart and with all your soul and with all your mind.’ This is the first and greatest commandment. And the second is like it: ‘Love your neighbour as yourself.’ (Matthew 22:37-39). So, sin is anything that we do or don’t do that means we fail to love God and our ‘neighbour’ (the meaning of neighbour here is broad and includes all people we come into contact with).
The Bible makes it clear that we all sin. All people fail to love God and our neighbour perfectly as our perfect God demands (Romans 3:9-12). The concern for humanity is that because God is perfect he cannot let sin go unpunished. But the good news for those who trust in Jesus and follow him as Lord, their sin is forgiven. This is because Jesus bore the punishment for our sin that we deserved when he died on the cross.
So while our sin is a reality and should concern us, there is good news.
“Brothers, listen! We are here to proclaim that through this man Jesus there is forgiveness for your sins. Everyone who believes in him is declared right with God’ Acts 13:38-39