Exceprt #2 from "The Reason for God" by Timothy Keller

The Difference of Grace
There is then, a great gulf between the understanding that God accepts us because our efforts and the understanding that God accepts us because of what Jesus has done. Religion operates on the principle "I obey--therefore I am accepted by God." But the operating principle of the gospel is "I am accepted by God through what Christ has done--therefore I obey." Two people living their lives on the basis of these two different principles may sit next to each other in the church pew. They both pray, give money generously, and are loyal to their family and church, trying to live decent lives. However they do so out of two radically different spiritual identities, and the result is two radically different kind of lives.
~ Timothy Keller from pages 179-180