Jonah 3:7

But it seems strange, and even ridiculous, that the king should bid animals, as well as men, to make a confession of repentance; for penitence is a change in man, when he returns to God after having been alienated from him: this cannot comport with the character of brute animals. Then the king of Nineveh acted foolishly and contrary to all reason in connecting animals with men when he spoke of repentance. But, in answer to this, we must bear in mind what I have before said — that destruction had been denounced, not only on men, but also on the whole city, even on the buildings: for as God created the whole world for the sake of men, so also his wrath, when excited against men, includes the beasts, and trees, and every thing in heaven and on earth. But the question is not yet solved; for though God may punish animals on account of men’s sins, yet neither oxen nor sheep can pacify the wrath of God. To this I answer — that this was done for the sake of men: for it would have been ridiculous in the king to prohibit food and drink to animals, except he had a regard to men themselves. But his object was to set before the Ninevites, as in a mirror or picture, what they deserved. The same was done under the law; for, whenever they slew victims, they were reminded of their own sins; for it ought to have come to their minds, that the sheep or any other animal sacrificed was innocent, and that it stood at the altar in his stead who had sinned. They therefore saw in the ox, or the lamb, or the goat, a striking emblem of their own condemnation. So also the Ninevites, when they constrained the oxen, the asses and other animals, to fast, were reminded of what grievous and severe punishment they were worthy: inasmuch as innocent animals suffered punishment together with them. We hence see that no expiation was sought for by the king, when he enjoined a fast on brute animals, but that, on the contrary, men were roused by such means seriously to acknowledge the wrath of God, and to entertain greater fear, that they might be more truly humbled before him, and be displeased with themselves, and be thus more disposed and better prepared and moulded to seek pardon.

We now then see that this must be considered as intended to terrify the consciences of men, that they, who had long flattered themselves, might by such a remedy be roused from their insensibility. The same was the intention of different washings under the law, the cleansing of garments and of vessels; it was, that the people might know that every thing they touched was polluted by their filth. And this ought to be especially observed; for the Papists, wedded as they are to external rites, lay hold on anything said in Scripture about fasting, and ashes, and sackcloth, and think that the whole of religion consists in these outward observances: but bodily exercise, as Paul says, profiteth but littler (1 Timothy 4:8.) Therefore this rule ought ever to be our guide — that fasting and such things are in themselves of no value, but must be estimated only by the end in view. So then, when the animals were constrained by the Ninevites to suffer want, the men themselves, being reminded of their guilt, learned what it was to dread God’s wrath; and on this account it was that fasting was approved by God.