Tim Keller has written a profound and insightful book, THE PRODIGAL GOD. Near the end he makes this observation [emphasis added]…

Religion operates on the principles of “I obey — therefore i am accepted by God.” The basic operating principle of the gospel is “I am accepted by God through the work of Jesus Christ — therefore I obey.” As we have seen, believing the gospel is how a person first makes a connection to God. It gives us a new relationship with God and a new identity. We must not think, however, that once believing it, the Christian is now finished with the gospel message. A fundamental insight of Martin Luther’s was that “religion” is the default mode of the human heart. Your computer operates automatically in a default mode unless you deliberately tell it to do something else. So Luther says that even after you are converted by the gospel your heart will go back to operating on other principles unless you deliberately, repeatedly set it to gospel-mode. [pp. 114-115]