Sin is a word used to describe those things which displease God. In all likelihood we will not use it, preferring instead the words right and wrong. It is easier to justify our actions and avoid shame if we can use our own moral standards.
It is vital we learn what God says is wrong as His opinion is the one that matters. For we must all appear before the judgment seat of Christ, so that each of us may receive what is due to us for the things done while in the body, whether good or bad (2 Corinthians 5:10).
What actions are sinful?
We cannot decide for ourselves what is good as we will inevitably get it wrong. We all, like sheep, have gone astray, each of us has turned to our own way... (Isaiah 53:6). Instead, we learn what actions are sinful by reading the Bible ...I would not have known what sin was had it not been for the law... (Romans 7:7).
It is easy to misunderstand the Bible and to get a wrong idea of sin, so we need to read it humbly. However, some passages are clear ...sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissentions, 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).
Sin is not just what we do, but includes our thoughts and motives, and what we say. But I tell you that everyone will have to give account on the day of judgment for every empty word they have spoken (Matthew 12:36).
The consequences of sin
Sin is contagious - it encourages those who do evil and discourages those who try to do good. It affects those around us - especially our families, our church and even our country. If rulers have a poor understanding of right and wrong, they will negatively affect the people they rule over. When the righteous thrive, the people rejoice; when the wicked rule, the people groan (Proverbs 29:2).
Once we sin, it is hard to stop. Jesus replied, 'Very truly I tell you, everyone who sins is a slave to sin...' (John 8:34). Sin needs to be corrected or worse things will happen. When the sentence for a crime is not quickly carried out, people's hearts are filled with schemes to do wrong (Ecclesiastes 8:11).
When we sin, we align ourselves with the devil. He who does what is sinful is of the devil...(1 John 3:8). This separates us from God and has serious consequences for us. For the wages of sin is death... (Romans 6:23).
Anyone wanting to live with God has to cope with His perfect standard of righteousness. Be perfect, therefore, as your heavenly Father is perfect (Matthew 5:48). Clearly, no one is able to do this, so God provides a way for us to come to Him and remain in His presence - know that a person is not justified by the works of the law, but by faith in Jesus Christ...(Galatians 2:16). If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness (1 John 1:9).