John Calvin
Where the Spirit of the Lord. He now describes the manner, in which Christ gives life to the law by giving us his Spirit. The term Spirit here has a different signification from what it had in the preceding verse. There, it denoted the soul, and was ascribed metaphorically to Christ. Here, on the other hand, it means the Holy Spirit, that Christ himself confers upon his people. Christ, however, by regenerating us, gives life to the law, and shows himself to be the fountain of life, as all vital functions proceed from man's soul. Christ, then, is to all (so to speak) the universal soul, not in respect of essence, but in respect of grace. Or, if you prefer it, Christ is the Spirit, because he quickens us by the lifegiving influence of his Spirit. [416]
John Calvin's Commentaries
http://biblehub.com/commentaries/calvin/2_corinthians/3.htm