The letter of the law as that which we see with our eyes the written law it is designed to kill .So it must be in respect to the spirit of the law called the law of faith.

Romans 2:27 And shall not uncircumcision which is by nature, if it fulfil the law, judge thee, who by the letter and circumcision (a ceremonial law) dost "transgress the law"?

Romans 2:29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, "in the spirit", and "not in the letter"; whose praise is not of men, but of God.

Romans 7:6 But now we are delivered from the law, that being dead wherein we were held; that we should serve in newness of spirit, and not in the oldness of the letter.

2Corinthians 3:6 Who also hath made us able ministers of the new testament; not "of the letter", but of the spirit: for the letter "killeth", but the spirit giveth life.