On the question why certain Names in the Holy Scriptures are changed (246-250)

Because, as the mind is the most excellent thing in us, so also is the sheep the most excellent among irrational animals, inasmuch as it is the most gentle, and also as it gives forth a yearly produce in its fleece, for the use and also for the ornament of mankind. For clothes keep off all injury from both cold and heat, and also they conceal the unmentionable parts of nature, and in this way they are an ornament to those who use them:

therefore the sheep, as being the most excellent of animals, is a symbol of the purification of the most excellent part of man, the mind. And birds are an emblem of the purification of the speech: for speech is a light thing, and winged by nature, flying and penetrating in every direction more swiftly than an arrow. For what is once said can never be re-called; [*] but being borne abroad, and running on with great swiftness, it strikes the ears and penetrates every sense of hearing, resounding loudly: but speech is of two kinds, one true and the other false;

on which account it appears to me to be here compared to a pair of turtle doves or young pigeons: and of these birds one he says is to be looked upon as a sin offering, and one is to be sacrificed as a burnt offering, since the speech which is true is wholly and in all respects sacred and perfect, but that which is false is very wrong and requires correction.

And he speaks with exceeding accuracy with respect to the sheep, when he says, "And if his hand be not strong enough to supply a sheep;" but with respect to the birds he says, "And if he cannot find a bird." Why is this? Because it is a sign of very great strength and of excessive power, to get rid of the errors of the mind: but it does not require any great strength, to check the errors of words;