32 The words of the Apostle are of like purport; For the Lord is Spirit, and where the Spirit of the Lord is, there is liberty. To make his meaning clear he has distinguished between the Spirit, Who exists, and Him Whose Spirit He is Proprietor and Property, He and His are different in sense. Thus when he says, The Lord is Spirit he reveals the infinity of God; when He adds, Where the Spirit of the Lord is, there is liberty, he indicates Him Who belongs to God; for He is the Spirit of the Lord, and Where the Spirit of the Lord is, there is liberty. The Apostle makes the statement not from any necessity of his own argument, but in the interests of clearness. For the Holy Ghost is everywhere One, enlightening all patriarchs and prophets and the whole company of the Law, inspiring John even in his mother's womb, given in due time to the Apostles and other believers, that they might recognise the truth vouchsafed them.
Source: On the Trinity (New Advent)