Evil of fault must not be done, that good may ensue; but evil of punishment must be inflicted for the sake of good.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic punishment evil
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“but that the blindness of others is directed to their loss is due to His justice: and that He vouchsafes His mercy to some, and not to all, does not make God a respecter of persons, as explained in the First Part (Q. 23, A. 5, ad 3) . Reply Obj. 4: Evil of fault must not be done, that good may ensue; but evil of punishment must be inflicted for the sake of good. ________________________ QUESTION 80 OF THE CAUSE OF SIN, AS REGARDS THE DEVIL (In Four Articles) We must now consider the cause of sin, as regards the devil; and under this head there are four points of inquiry:” source