What is the essence of sin? There are bound to be lots of questions like "Is X or Y a sin?". However, what is sin at its root and where in the Bible do we get our understanding of it?
Luther has famously argues that every time you break any other commandment, you always break the first commandment; in other words, behind every sin is the desire to worship a god other the God. Whether it is pride, in which we consider ourself to be God, or a sin of fear-of-man, in which we consider another person to be God, all sin is, at its core, idolatry.

When you see the essential problem as a worship issue, over against a breaking-of-commandments issue, I think several things are clarified.


Worship and idolatry addresses both the positive and negative sides. That is, when we do what is right, we are worshipping God (and conversely), and when we are not worshipping God, we are not doing what is right (and conversely).
Much of the Bible talks about idolatry, and seems a bit foreign and obsolete to modern ears. After all, we do not deal with Baal or Molech on a daily basis. However, when considering this as an example of our basic relationship with God, these passages become much more relavant. God is repeatedly enraged by his people worshipping idols and intermixing with other gods. Though we do not by and large bow down to physical idols made by hands, we do worship at the gods of money, power, etc.
The idolatry issues allows for a distinction between things that are good and created by God against things that ultimate for us. God gives us food, but we can be gluttons. God gives us sex but we find all ways to abuse it. Seeing sin as essentially idolatry allows us to have good things be God-centered, and not find abuse to be the only use we can comprehend.