From: letusreason.org/Biblexp4.htm

* 2 Corinthians 3:6 (The letter killeth, but the spirit giveth life) is allegorized in its interpretation to mean that Scripture is a dead letter and only the Spirit is what is important. So we need to heed new and fresh words from the Spirit [we do need to hear the Holy Spirit directly as well as acknowledging the Holy Spirit’s teaching in the New Testament – editor]. But this is not what the Apostle Paul is saying. Again if we read it in context (before and after the portion that is lifted out to mean something other than the author wrote) we find the true meaning.

2 Corinthians 3:6-8 “who also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life. But if the ministry of death, written and engraved on stones, was glorious, so that the children of Israel could not look steadily at the face of Moses because of the glory of his countenance, which glory was passing away, how will the ministry of the Spirit not be more glorious?

Paul is making a distinction between the Old Covenant written on stone and the New Covenant that is presented inside us by the Spirit. The old (the law) brought death, because no one could keep its directives, whereas the new brings life through the life-giving Spirit. The letter (the law) killed because no one was able to keep it. It made us guilty, while the New Covenant sets us free from the condemnation of the law [when we obey and overcome through God’s grace, the Holy Spirit now living inside of us – editor]. The law was fulfilled in the only person who could have fulfilled it, the God/man Jesus Christ. Now we have the spirit of God inside us all because of this new covenant that is superior to the old covenant.