Letter

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. (See WRITING T0003841.)