The letter is the outer, literal reading of Scripture taken as far-off history, and it kills because it holds a person on the surface, chained to events and places outside himself. The spirit is the hidden meaning folded inside the same words, the account of the body and consciousness the writers concealed, and it gives life because it turns the whole book inward where the change actually happens.
To minister the spirit rather than the letter is to read every story as something occurring now inside a person. The words stay the same; life or death depends on whether they are read outwardly or within.
Letter: the outer, literal reading held as distant history, keeping a person on the surface
Spirit: the hidden inner meaning folded in the same words, the account of the body read within