The greatest sin a man can commit is DISOBEDIENCE to God. The act of disobedience makes you break the rules of God. The sole aim of Satan is to have man disobey God like he did in the garden of Eden.
1 Samuel 15:22-23
22 And Samuel said, has the LORD has great delight in burnt offerings and sacrifices, as in obeying the voice of the LORD? Behold, to obey is better than sacrifice, and to hearken than the fat of rams
23 For rebellion is as the sin of witchcraft, and stubbornness is as iniquity and idolatry. Because thou hast rejected
the word of the LORD, he hath also rejected thee from being king
In the Ten Commandments, God said you should not do this and you should not do that. There are other places in the Bible where God said we should not do other things apart from the ones mentioned in the Exodus 20. The life of Israelites/Christian is based on following God's detail instructions. In the passage mentioned above, Saul was the victim.
In this new age, our daily living and place in christ is centered around hearing from him and following his lead
1 As for you, you were dead in your transgressions and sins,
2 in which you used to live when you followed the ways of
this world and of the ruler of the kingdom of the air, the spirit who
is now at work in those who are disobedient
This is God's commandment to everybody
Mark 9:7 And there was a cloud that overshadowed them: and a voice came out of the cloud, saying, This is my beloved Son: hear him
Jesus also said in John 10:27
My sheep hear my voice, and I know them, and they
To follow somebody's lead you have to obey them
Romans 8:14 For as many as are led by the Spirit of God, they are the sons of God
Simply disobeying God makes it the greatest sin of all time. It was the first sin, committed by the first man. It was what took them out of the garden. It was what took Satan out of heaven.