Consequently, if the demons have faith, some men would be guilty of a sin graver than that of the demons, which seems unreasonable. Therefore in the demons there is no faith.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic faith sin
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/18755/pg18755-images.html

Context

“3: Further, unbelief would seem to be graver than other sins, as Augustine observes (Tract. lxxxix in Joan.) on John 15:22, "If I had not come and spoken to them, they would not have sin: but now they have no excuse for their sin." Now the sin of unbelief is in some men. Consequently, if the demons have faith, some men would be guilty of a sin graver than that of the demons, which seems unreasonable. Therefore in the demons there is no faith. On the contrary, It is written (James 2:19) : "The devils.. . believe and tremble."
I answer that, As stated above (Q. 1, A. 4; Q. 2, A. 1) , the believer's intellect assents to that which he believes, not because he sees it either in itself, or by resolving it to first self-evident principles, but because his will commands his intellect to assent.” source