Sin as Selfishness

All sin can be boiled down to one concept, selfishness. All sinful actions are the result of selfishness and have their root in selfishness. The selfish, ego driven person sins again and again. The ten commandments would have been the most unnecessary rules for living had man not been a selfish being. If you read the ten commandments they are all warnings against selfish behaviors. A person who lies is being selfish. They only care about preserving and protecting themselves and what is inevitabley a false identitiy. The person who steals is operating with the idea that what they want is the most important thing and anything done to fulfill that want is justified as long as it benefits them. Killing is a selfish act. Think about the other commandments and you will see that they are all warnings against a egocentric world view.
Jesus' entire teaching was against selfishness hence him saying, "My kingdom is not of this world." John 18:36 The main teachings of Jesus centered around forgiveness, love, compassion, and renunciation of worldly treasures. All of these things take a unselfish and altruistic person to fulfill.
Buddhism doesn't have sin in the same way that Christianity does but the law of karma is a very close relative. Karma is plain to see; negative thoughts and actions produce negative results. All bad karma is the result of the false view that there is a tangible self that exists seperate from the world and the desire to preserve this sense of self. Bad karma = selfish action. When we act out of loving kindness, operate from a position of understanding and forgiveness good things naturally flow into our life. The person with few desires and wants is liberated and happy knowing they have what they need.