Yes, the greatest sin in the world is the sin that master you day by day.
It is somehow improper to clasify the sins, although we must admit that there exist bigger and smaller sins, but all have the same effect: they separate us from God and then we remain without His help and. Also our sins influence people around us.
In vain I judge others for adultery, murder or other sins, because I am in the same situation commiting different sins. For me eating in excess is like adultery for the others. For me to abstain from eating to excess is as hard as when someone wants to abstain from adultery. It is easy for me not to get angry but it is hard to shut up, not to brag, not to judge…
The greatest sin in the world is, actually mine… my greatest sin. And if God will help me to get rid of it, there will appear another great sin that will keep me bound to the earth and to the body.
As the commandament of God is only one : „And thou shalt love the Lord thy God, with thy whole heart, and with thy whole soul, and with thy whole mind, and with thy whole strength. And to love your neighbor as yourself.” So the sin is in fact only one. It is actually a violation of this commandament.
„For the person who keeps all of the laws except one is as guilty as a person who has broken all of God’s laws. For the same God who said, “You must not commit adultery,” also said, “You must not murder.”So if you murder someone but do not commit adultery, you have still broken the law. So whatever you say or whatever you do, remember that you will be judged by the law that sets you free. There will be no mercy for those who have not shown mercy to others. But if you have been merciful, God will be merciful when he judges you.”