'Letter' in the Bible

and uncircumcision by nature, fulfilling the law, judge thee, who, with letter and circumcision, art a law-transgressor?

but he is a Jew who is so inwardly; and circumcision, of the heart, in spirit, not in letter; whose praise is not of men, but of God.

but now we are clear from the law, having died in that in which we were held, so that we should serve in newness of spirit, and not in oldness of letter.