Yes, the greatest sin in the world is the sin which dominates you every day.
It is kind of inappropriate to make a classification of sins, although we must admit that there are severe and less severe sins, but they all have the same effect: they alienate us from God and leave us without His help and indirectly affect the others.
It is pointless for me to judge the others for committing fornication, murder, for remaining in severe sins while I am just like them, except for the fact that I remain in other kinds of sins. Overeating is for me just as fornication is for others. For me it is as hard to restrain from eating as it is for somebody else to abstain from physical relations. It is often easy for me not to get mad but I find it hard to keep quiet, it is hard for me not to brag, not to judge…
The greatest sin in the world is actually my greatest sin. And if God helps me get rid of it, a different very severe sin will arise out of the load of sins left which keep me chained down to earth and to my body.
The same way that God’s command is one: ‚Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength, and your neighbor as yourself’, sin is also one, it is actually the breach of this command. Thus sins are not more or less severe but they are all breaches of commands.
For whoever will observe the whole law but will have offended in one, has become guilty of all. For He who said: ‘You shall not commit adultery’ also said: ‘You shall not murder’. And if you don’t commit adultery but you do commit murder, you have become a transgressor of the law. Speak and act as those who are going to be judged by the law that gives freedom. Because judgment without mercy will be shown to anyone who has not been merciful. And mercy triumphs over judgement.
Translated by Claudia