How spirit cannot be penetrated by spirit, and how God alone is incorporeal.
For even if spirit is mingled with this crass and solid matter; viz., flesh (as very easily happens), should we therefore believe that it can be united to the soul, which is in like manner spirit, in such a way as to make it also receptive in the same way of its own nature: a thing which is possible to the p. 367 Trinity alone, which is so capable of pervading every intellectual nature, that it cannot only embrace and surround it but even insert itself into it and, incorporeal though it is, be infused into a body? For though we maintain that some spiritual natures exist, such as angels, archangels and the other powers, and indeed our own souls and the thin air, yet we ought certainly not to consider them incorporeal. For they have in their own fashion a body in which they exist, though it is much finer than our bodies are, in accordance with the Apostles words when he says: “And there are bodies celestial, and bodies terrestrial:” and again: “It is sown a natural body, it is raised a spiritual body;” 1471 from which it is clearly gathered that there is nothing incorporeal but God alone, and therefore it is only by Him that all spiritual and intellectual substances can be pervaded, because He alone is whole and everywhere and in all things, in such a way as to behold and see the thoughts of men and their inner movements and all the recesses of the soul; since it was of Him alone that the blessed Apostle spoke when he said: “For the word of God is quick and powerful and sharper than any two-edged sword, and piercing even to the dividing of soul and spirit and of the joints and marrow; and is a discerner of the thoughts and intents of the heart; and there is no creature invisible in His sight, but all things are naked and open to His eyes.” 1472 And the blessed David says: “Who fashioneth their hearts one by one;” and again: “For He knoweth the secrets of the heart;” 1473 and Job too: “Thou who alone knowest the hearts of men.” 1474
1 Cor. 15:40, 44.367:1472
Heb. 4:12, 13.367:1473
Ps. 33:15, Ps. 44:22.367:1474
2 Chron. vi. 30.