Job 6:5

The objection could be made: you certainly have cause for suffering, but you should not burst out in words of pain from it. Against this objection Job responds using examples which are found in other animals. For man is like other animals in sensitive nature, …

By mentioning the wild ass, the author speaks about all wild animals, and by referring to the ox, about all cattle. His point is that neither wild animals nor cattle complain when they have food to eat. Nor do humans complain when they can have …

MORAL INTERPRETATION Doth the wild ass bray when he hath grass? Or loweth the ox over his full manger? Who else are denoted by the term of 'the wild ass,' saving they who being set in the field of faith, are not bound by the reins of any ministration? Or whom does the designation of 'the ox' set forth, saving those, whom within the bounds of Holy Church, the yoke of Orders taken upon them constrains to the ministry of preaching? Now the 'grass' of the wild ass, and the ox's 'fodder,' is the inward refreshing of the faithful folk. For some within the pale of Holy Church are held after the manner of an ox by the bands of the employment taken upon them, others after the manner of a 'wild ass' know nothing of the stalls of Holy Orders, and pass their time in the field of their own will. But when any one in the secular life glows with aspirations after the interior vision, when he yearns for the food of the inward refreshing, when seeing himself starved in the darkness of this pilgrim state, he refreshes himself with what tears he may, it is as if 'the wild ass brayed,' not finding 'grass.' Another one too is subject to the obligation of the Order he has taken upon him, he spends himself in the labour of preaching, and longs to be henceforth refreshed by eternal contemplation; but forasmuch as he does not see the likeness of His Redeemer, it is as if the chained ox lowed at the empty manger. For because being set at the widest distance from the interior wisdom, we see nothing of the verdure of the eternal inheritance, like brute animals we go hungering after the longed for grass. Of which same grass it is said by the voice of our Redeemer, By Me if any man enter in, he shall be sated, and shall go in and out, and find pasture. […]

Doth the wild ass bray when he hath grass? or loweth the ox at his full manger? ALLEGORICAL INTERPRETATION For what is denoted by 'the onager,' that is, the wild ass, saving the Gentile people, which, as nature has produced it without the stalls of training, so has continued roaming abroad in the field of its pleasures? What is represented by 'the ox,' saving the Jewish people, which being bowed down to the yoke of the dominion above, in gathering together proselytes unto hope, drew the ploughshare of the Law through all the hearts that it was able?

Doth, &c. - Even the brute beasts, when they have convenient food, are quiet and contented. So it is no wonder that you complain not, who live in ease and prosperity, any more than I did, when I wanted nothing.