Wherefore, as every sin is against God, and since no work is acceptable to God unless it be virtuous, it follows that nothing unlawful or indifferent, but only some act of virtue, should be the matter of a vow.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic virtue 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

“Now a promise is about something that one does voluntarily for someone else: since it would be not a promise but a threat to say that one would do something against someone. In like manner it would be futile to promise anyone something unacceptable to him. Wherefore, as every sin is against God, and since no work is acceptable to God unless it be virtuous, it follows that nothing unlawful or indifferent, but only some act of virtue, should be the matter of a vow. But as a vow denotes a voluntary promise, while necessity excludes voluntariness, whatever is absolutely necessary, whether to be or not to be, can nowise be the matter of a vow. For it would be foolish to vow that one would die or that one would not fly.
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