At the heart of Redeemer’s ministry and its philosophy of preaching to post-modern audiences is the conviction that “the gospel” is not just a way to be saved from the penalty of sin, but is the fundamental dynamic for living the whole Christian life–individually and corporately, privately and publicly. In other words, the gospel is not just for non-Christians, but also for Christians. This means the gospel is not just the A-B-C’s but the A to Z of the Christian life. It is not accurate to think ‘the gospel’ is what saves non-Christians, and then, what matures Christians is trying hard to live according to Biblical principles. It is more accurate to say that we are saved by believing the gospel, and then we are transformed in every part of our mind, heart, and life by believing the gospel more and more deeply as our life goes on.
Taken from Keller’s article “PREACHING THE GOSPEL AS THE KEY FOR CHRISTIANS”