The Hebrew word for sin is chata. The first time a form of it is used is in Genesis 4:7 when God tells Cain, “If you do well, will you not be accepted? And if you do not do well, sin (chatta'ah) is crouching at the door. Its desire is for you, but you must rule over it.”
Therefore, we must begin with the understanding that the word sin is God's word, not ours. He was the first to use it, not us. When he spoke it, he was communicating something to us. The question is what. The answer lies in God's use of it. Frequently God graciously defines His own words within His statement. In regards to chatta'ah he defines it this way, “If you do not do well.” Therefore, it appears that God is saying that not doing well is sin.
However, this begs the question, who determines what behavior is well or not well? God of course. It is God who is evaluating the behavior of Cain. God is determining what behavior is acceptable and unacceptable. Cain missed the mark, and Able did not; therefore God was pleased with Able and not with Cain.
So how does this help with understanding what sin is. It helps because sin is sin because God deems it to be sin. God is the standard giver. He is the one who determines what is right and what is wrong. He is he one that draws the line in the sand and says, “Do not cross.”
This is a reality that many people forget. In this day in age people seem to evaluate sin democratically. We informally take votes as to what is right and what is wrong. If a vast majority of people are comfortable with a certain standard of behavior then we draw a new line in the sand. We forget that we are not God, and we do not create standards, but submit to them.
How many times have you heard someone say, “I don't see anything wrong with it.” This statement is extremely conceded, for this person is putting themselves in the place of God. They view themselves as the evaluator of what is sin and what is not sin. They are the ones drawing the line in the sand. They are the ones who are determining the standard. They are deciding what God should accept. However, that is not how sin is determined.
For example the first sin was eating a certain food from a certain tree. What made eating this food so bad? I mean...what is wrong with food? If you desire food and it makes you happy, why shouldn't you be able to eat whatever you want, whenever you want, with whomever you want. How is eating food hurting anyone? Shouldn't they be able to eat whatever they want in the privacy of their own home? No because God said don’t' do it. This is why eating from that tree was sin. This is the only reason it is sin.
This applies for all sins. Why is lying a sin? Because God says it is. Why is lusting in your heart a sin? Because God says it is. Why is saying the Lord's name in vain a sin? Because God says it is. Why is gossip a sin? Because God says it is. Why is homosexuality a sin? Because God says it is. The concept is not complicated. God is the one who determines what is right and what is wrong Sin is not relative, cultural, evolving, or up to us. Sin is missing the mark that God has set in place.
Lastly, and most importantly, we must heed the words of God as spoken to Cain, “sin is crouching at the door. Its desire is for you, but you must rule over it.” First we must recognize sin for what it is and second we must rule over it. How? Jesus Christ. “If we say we have no sin, we deceive ourselves, and the truth is not in us. 9If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. “ (1 John 1:9)