For the human soul is not capable of sin nor of justifying grace except through the mind.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic sin mind
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/19950/pg19950-images.html

Context

“inasmuch as when we see an effect and are ignorant of its cause, we seek to know it, as is said Metaph. i, 2. Secondly, it is inconsistent with the purpose of the Incarnation, which is the justification of man from sin. For the human soul is not capable of sin nor of justifying grace except through the mind. Hence it was especially necessary for the mind to be assumed. Hence Damascene says (De Fide Orth. iii, 6) that "the Word of God assumed a body and an intellectual and rational soul," and adds afterwards:” source