2 Corinthians 3:6

Here the apostle makes a comparison between the Old Testament and the New, the law of Moses and the gospel of Jesus Christ, and values himself and his fellow-labourers by this, that they were able ministers of the New Testament, that God had made them so, Co2 3:6. This he does in answer to the accusations of false teachers, who magnify greatly the law of Moses. I. He distinguishes between the letter and the spirit even of the New Testament, Co2 3:6. As able ministers of the New Testament, they were ministers not merely of the letter, to read the written word, or to preach the letter of the gospel only, but they were ministers of the Spirit also; the Spirit of God did accompany their ministrations. The letter killeth; this the letter of the law does, for that is the ministration of death; and if we rest only in the letter of the gospel we shall be never the better for so doing, for even that will be a savour of death unto death; but the Spirit of the gospel, going along with the ministry of the gospel, giveth life spiritual and life eternal. II. He shows the difference between the Old Testament and the New, and the excellency of the gospel above the law. For, 1. The Old Testament dispensation was the ministration of death (Co2 3:7), whereas that of the New Testament is the ministration of life.

— Matthew Henry's Concise Commentary (public domain)

able--rather, as the Greek is the same, corresponding to Co2 3:5, translate, "sufficient as ministers" (Eph 3:7; Col 1:23). the new testament--"the new covenant" as contrasted with the Old Testament or covenant (Co1 11:25; Gal 4:24). He reverts here again to the contrast between the law on "tables of stone," and that "written by the Spirit on fleshly tables of the heart" (Co2 3:3). not of the letter--joined with "ministers"; ministers not of the mere literal precept, in which the old law, as then understood, consisted; "but of the Spirit," that is, the spiritual holiness which lay under the old law, and which the new covenant brings to light (Mat. 5:17-48) with new motives added, and a new power of obedience imparted, namely, the Holy Spirit (Rom 7:6). Even in writing the letter of the New Testament, Paul and the other sacred writers were ministers not of the letter, but of the spirit. No piety of spirit could exempt a man from the yoke of the letter of each legal ordinance under the Old Testament; for God had appointed this as the way in which He chose a devout Jew to express his state of mind towards God. Christianity, on the other hand, makes the spirit of our outward observances everything, and the letter a secondary consideration (Joh 4:24).

— Jamieson-Fausset-Brown Commentary (public domain)