Elisabeth Elliot's book Keep a Quiet Heart discusses what she calls "the Jesus Prayer."
The prayer arose over 1,000 years ago. It goes like this: "Lord Jesus Christ, Son of God, have mercy on my a sinner." It's easy to see why this prayer has endured. Its single request is a wonderful summary of everything a believer might ask of the Lord -- "Have mercy on me." We all are truly sinners. We have no claim on forgiveness except through the pure, shining mercy of God. Elisabeth Elliot notes that when her husband was dying of cancer, they often prayed the Jesus Prayer together. She concludes: "I recommend it to you."
So do I.