23 You have seen His power, which is in all the world; tarry now no longer upon earth, but ascend on high. Ascend, I say, in imagination even unto the first heaven, and behold there so many countless myriads of Angels. Mount up in your thoughts, if you can, yet higher; consider, I pray you, the Archangels, consider also the Spirits; consider the Virtues, consider the Principalities, consider the Powers, consider the Thrones, consider the Dominions —of all these the Comforter is the Ruler from God, and the Teacher, and the Sanctifier.
Of Him Elias has need, and Elisseus, and Esaias, among men; of Him Michael and Gabriel have need among Angels. Naught of things created is equal in honour to Him: for the families of the Angels, and all their hosts assembled together, have no equality with the Holy Ghost. All these the all-excellent power of the Comforter overshadows. And they indeed are sent forth to minister, but He searches even the deep things of God, according as the Apostle says, For the Spirit searches all things, yea, the deep things of God. For what man knows the thing of a man, save the spirit of the man which is in him? Even so the things of God knows no man, but the Spirit of God.
Source: Catechetical Lectures (New Advent)