What is sin?

What is sin?
To sin is to go against God. Since God is love, to go against love-which is to be selfish, is to sin. Jesus showed us what true love is. He loved us first; without expecting anything in return. He loved us by sacrificing His life in order to compensate for our sins; although we betrayed Him and was unfaithful to Him. Only this kind of love is free of selfishness or sin. Therefore, to be free of sin we must love God and our fellow human being unconditionally.