Now this relates not to falsehood. For not every thing we feign is a falsehood, but only when we feign that which means nothing. But when our feigning has reference to a certain meaning it is not a falsehood, but a kind of figure of the truth. Otherwise all the things figuratively spoken by wise and holy men, or even by our Lord Himself, must be accounted falsehoods. For to the experienced understanding truth consists not in certain words, but as words so also deeds are feigned without falsehood to signify a particular thing.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: de Qu. Ev. lib. ii. c. 51.