Obj. 3:  Further, the knowledge of faith and the knowledge of glory differ as perfect from imperfect.  Now imperfect knowledge is compatible with perfect knowledge:  thus in an angel there can be “evening” and “morning” knowledge [Cf.  I, Q. 58, A. 6]; and a man can have science through a demonstrative syllogism, together with opinion through a probable syllogism, about one same conclusion.  Therefore after this life faith also is compatible with the knowledge of glory.

On the contrary, The Apostle says (2 Cor. 5:6, 7):  “While we are in the body, we are absent from the Lord:  for we walk by faith and not by sight.”  But those who are in glory are not absent from the Lord, but present to Him.  Therefore after this life faith does not remain in the life of glory.

I answer that, Opposition is of itself the proper cause of one thing being excluded from another, in so far, to wit, as wherever two things are opposite to one another, we find opposition of affirmation and negation.  Now in some things we find opposition in respect of contrary forms; thus in colors we find white and black.  In others we find opposition in respect of perfection and imperfection:  wherefore in alterations, more and less are considered to be contraries, as when a thing from being less hot is made more hot (Phys. v, text. 19).  And since perfect and imperfect are opposite to one another, it is impossible for perfection and imperfection to affect the same thing at the same time.

Now we must take note that sometimes imperfection belongs to a thing’s very nature, and belongs to its species:  even as lack of reason belongs to the very specific nature of a horse and an ox.  And since a thing, so long as it remains the same identically, cannot pass from one species to another, it follows that if such an imperfection be removed, the species of that thing is changed:  even as it would no longer be an ox or a horse, were it to be rational.  Sometimes, however, the imperfection does not belong to the specific nature, but is accidental to the individual by reason of something else; even as sometimes lack of reason is accidental to a man, because he is asleep, or because he is drunk, or for some like reason; and it is evident, that if such an imperfection be removed, the thing remains substantially.

Now it is clear that imperfect knowledge belongs to the very nature of faith:  for it is included in its definition; faith being defined as “the substance of things to be hoped for, the evidence of things that appear not” (Heb. 11:1).  Wherefore Augustine says (Tract. xl in Joan.):  “What is faith?  Believing without seeing.”  But it is an imperfect knowledge that is of things unapparent or unseen.  Consequently imperfect knowledge belongs to the very nature of faith:  therefore it is clear that the knowledge of faith cannot be perfect and remain identically the same.