For the letter kills, but the Spirit gives life. (2 Cor. 3:6b)
Such is the confidence that we have through Christ toward God. Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God, who has made us competent to be ministers of a new covenant, not of the letter but of the Spirit. For the letter kills, but the Spirit gives life. (2 Cor. 3:4-6)
In mystical and especially charismatic circles, 2 Cor. 3:6b is used to promote their anti-intellectualism. Equating the letter with the written words of Scripture or the "logos Word", these mystics contrasts those "dead words" with the living Holy Spirit or the "rhema Word". Therefore, the important thing is to keep close to the Spirit, and not to allow "dry" doctrines and theology to interfere with the Spirit's voice. Coupled together with this theory is the assertion that the sin of the Pharisees was that they were too knowledgeable and doctrinal, conveniently omitting Scripture such as Jn. 3:10 for example that shows that the Pharisees were actually spiritually ignorant.
The words logos and rhema has been shown to be essentially the same with huge semantic overlap between them [see Gordon H. Clark, The Johannine Logos (Jefferso, Maryland, USA: Trinity Foundation, 1989), p. 46, 51, 57], thus the charismatic confusion on this matter is lamentable. Yet, the focus here is not so much refutation of the charismatic position but rather the interpretation of 2 Cor. 3:6b.
When we look at the context, it should be immediately seen that the words "letter" and "Spirit" are not just referring to themselves. The whole context of 2 Cor. 3 is on the New Covenant, and in contrasting the Old Covenant with the New. Following from verse 5 and 6a therefore, we can see that the "letter" is analogous to the Old Covenant that was fixed and rigidly carved on stone, while the "Spirit" is analogous to the New Covenant with its fuller reality of the Holy Spirit. Therefore, the phrase should better read thus:
The Old Covenant kills, but the New Covenant gives life
Far from it therefore for the "letter" to refer to "soulish" doctrines and theology, while the Spirit represents the "spiritual" knowledge given by the Spirit. The verse is actually contrasting two covenants, and thus two ways of life. We should not be living by the "letter", as that would be to go back to the Old Covenant, but we should be in the New Covenant, and thus living by the Spirit.
In conclusion, 2 Cor. 3:6b in context is actually on soteriology, not mystical knowledge. Doctrines are indeed good and necessary, and we should never think of divorcing the Word and the Spirit. Amen.