This is, perhaps, my favorite story on discipleship. I've used it in many sermons and illustrations. I think it sums up the Christian life nicely is true to the entire witness of Holy Scripture. I can't take credit for it. I read it in Joan Chittister's book on the Rule of Benedict.
There was a young novice monk who came to the Master of Novices and asked: "Master, what must I do to attain God?"
The master looked at the young monk and said: "To attain God, you must do two things."
"Two things" the novice thought to himself. "This is going to be easy!"
"First", continued the Master, "You must know that nothing you can do or say or think will ever help you to attain God."
"And the second?" replied the crestfallen novice.
"You must live as if you don't know the first" said the Master.
The Christian life is a life lived in God's grace and empowered by God's grace and lived through faith. Faith is not a simple mental assent to a set of theological propositions. It is an active trust that God knows better than we do and that God wills better for us than we can imagine. We are saved by the life, death, resurrection, and ascension of Jesus Christ. Nothing we do can ever bring us salvation or increase God's grace in us. It is all God's grace.
On the other hand, we must actively seek His grace. We must exercise our "faith muscles" so that we trust God more and more and depend on His grace more and more and on ourselves less and less.
So the question comes up: "What can I do to be saved?" The answer is "nothing you can do will ever earn salvation. The next question comes up: "What do I do in response to that?" The answer is "Everything in your power."