The gospel is radically different from religion. Religion operates on the principle: “I obey, therefore I am accepted”. The gospel operates on the principle: “I am accepted through Christ, therefore I obey.” So the gospel differs from both religion and irreligion. Not only can you seek to be your own ‘lord and savior’ by breaking the law of God (i.e., through irreligion), you can also do so by keeping the law in order to earn your salvation (i.e., through religion). A lack of deep belief in the gospel is the main cause of spiritual deadness, fear, and pride in Christians, because our hearts continue to act on the basis “I obey, therefore, I am accepted.” If we fail to forgive others–that is not simply a lack of obedience, but a failure to believe we are saved by grace, too. If we lie in order to cover up a mistake–that is not simply a lack of obedience, but a failure to find our acceptance in God rather than in human approval. So we do not ‘get saved’ by believing the gospel and then ‘grow’ by trying hard to live according to Biblical principles. Believing the gospel is not only the way to meet God, but also the way to grow into him.
– Tim Keller