A well-stated answer to the question from the below referenced resource:

"The gospel transforms us in heart, mind, will, and actions precisely because it is not itself a message about our transformation. Nothing that I am or that I feel, choose, or do qualifies as Good News. On my best days, my experience of transformation is weak, but the gospel is an announcement of a certain state of affairs that exists because of something in God, not something in me; something that God has done, not something that I have done; the love in God’s heart which he has shown in his Son, not the love in my heart that I exhibit in my relationships. Precisely as the Good News of a completed, sufficient, and perfect work of God in Christ accomplished for me and outside of me in history, the gospel is ‘the power of God unto salvation’ not only at the beginning but throughout the Christian life. In fact, our sanctification is simply a lifelong process of letting that Good News sink in and responding appropriately; becoming the people whom God says that we already are in Christ."

Michael Horton, The Gospel-Driven Life (Grand Rapids, Mi.: Baker Books, 2009), p. 77