Why the Gospel isn't just for the lost, but for the saved too

From Pastor Tim Keller:
Paul said to the Corinthians, "I gave you birth through the gospel"! And then, after it has regenerated us, it is the instrument of all continual growth and spiritual progress after we are converted. "All over the world this gospel is bearing fruit and growing, just as it has been doing among you since the day you heard it and understood God's grace in all its truth." (Col. 1:6). Here we learn:

1. That the gospel is a living thing (cf. Romans 1:16) which is like a seed or a tree that brings more and more new life--bearing fruit and growing.
2. That the gospel is only "planted" in us so as to bear fruit as we understand its greatness and implications deeply--understood God's grace in all its truth.
3. That the gospel continues to grow in us and renew us throughout our lives--as it has been doing since the day you heard it.

This text helps us avoid either an exclusively rationalistic or mystical approach to renewal. On the one hand, the gospel has a content--it is profound doctrine. It is truth, and specifically, it is the truth about God's grace. But on the other hand, this truth is a living power that continually expands its influence in our lives, just as a crop or a tree would grow and spread and dominate more and more of an area with roots and fruit.

The full essay can be obtained here: The Centrality of the Gospel