Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
In Rom. 2:27, 29 means the outward form. The "oldness of the letter" (7:6) is a phrase which denotes the old way of literal outward obedience to the law as a system of mere external rules of conduct. In 2 Cor. 3:6, "the letter" means the Mosaic law as a written law.