There are 3 powerful words that describe the condition of the believer who is taking advantage of his privileges in Christ Jesus--rest, peace, and joy. These three words are the fruit of full grown faith. "Peace I leave with you, my peace I give unto you: not as the world giveth, give I unto you. Let not your heart be troubled, neither let it be afraid (John 14:27). This peace didn't belong to the Jews under the first covenant. The only peace they new would be a national peace, but with the New Creation, it is a peace of the heart, a peace of mind, a peace in his physical body. Sickness is called disease, broken peace, broken rest, broken joy.
Isaiah 26:3 is a prophecy of the church, "Thou wilt keep him in perfect peace whose mind is stayed on thee because he trusteth in thee".