Gregory the Great

If we carefully examine the words of the Prophets, we discover that these and they were put forth by the same Spirit. For when Isaiah observed the life of sinners devoured by the ancient and insatiable enemy, he said, "the lion shall eat straw like the ox." But what is signified by the words hay, and straw, except the life of the carnal? Of which it is said by the Prophet, "All flesh is hay." He then who here is 'Behemoth,' is there a 'lion;' they who are here called 'hay,' are there called 'straw.' But the mind strives to enquire why this lion in Isaiah, or Behemoth as he is called by the voice of the Lord, is in both passages compared not to a horse, but an ox. But we ascertain this the sooner, if we consider what is the difference of foods in the two animals. For horses eat hay, however dirty, but drink clean water only. But oxen drink water, however filthy, but feed only on clean hay. What then is it, for which this Behemoth is compared to an ox, which feeds on clean food, except that which is said of this ancient enemy by another Prophet: "His food is choice." For he rejoices not in seizing those whom he beholds lying of their own accord in the lowest depths with himself, involved in wicked and filthy actions. He therefore seeks to eat hay as an ox, because he seeks to wound with the fang of his suggestion the pure life of the spiritual.