The following quotations are from today's entry for Journey to the Cross, Haug and Walker:

"Everlasting God, fountain of all life and the true home of every heart: our hearts are restless until they find rest in you. Yet we confess that our hearts have been enslaved by selfish passion and base desire. We have sought after many things and have neglected the one thing needful." (The Worship Sourcebook) 

"Sin is the despairing refusal to find your deepest identity in your relationship and service to God. Sin is seeking to become oneself, to get an identity, apart from God."(Soren Kierkegaard) 

"Sin is not just the doing of bad things, but the making of good things into ultimate things. It is seeking to establish a sense of self by making something else more central to your significance, purpose, and happiness than your relationship with God." (Tim Keller) 

"This is a meaningful way to think about sin because we all identify with trying to build our identity on something. In our culture it tends to be things like achievements, or relationships, or being thought of as a good Christian. Everyone is building his or her identity on something.
In my experience of trying to establish myself on the basis of other people's approval, I found it to be an exhausting and frustrating endeavor. This is what St. Augustine meant when he said, "We were made for God, and that our hearts are restless until they find rest in him." [sic] 

. . .  

The gospel sets us free from this kind of fickle faith. God approves of us in Christ, without condition. We are accepted and adopted into his family. We don't need anything more than what we have been given in Christ. We cannot accomplish anything more than what he has already done on our behalf. Nothing can separate us from the love of God. Therefore, we are free to accept responsibility for our sin without fear of condemnation."