2 “Let the earth bring forth the living creature.” Behold the word of God pervading creation, beginning even then the efficacy which is seen displayed today, and will be displayed to the end of the world! As a ball, which one pushes, if it meet a declivity, descends, carried by its form and the nature of the ground and does not stop until it has reached a level surface; so nature, once put in motion by the Divine command, traverses creation with an equal step, through birth and death, and keeps up the succession of kinds through resemblance, to the last. Nature always makes a horse succeed to a horse, a lion to a lion, an eagle to an eagle, and preserving each animal by these uninterrupted successions she transmits it to the end of all things. Animals do not see their peculiarities destroyed or effaced by any length of time; their nature, as though it had been just constituted, follows the course of ages, for ever young. “Let the earth bring forth the living creature.” This command has continued and earth does not cease to obey the Creator. For, if there are creatures which are successively produced by their predecessors, there are others that even today we see born from the earth itself. In wet weather she brings forth grasshoppers and an immense number of insects which fly in the air and have no names because they are so small; she also produces mice and frogs. In the environs of Thebes in Egypt, after abundant rain in hot weather, the country is covered with field mice. We see mud alone produce eels; they do not proceed from an egg, nor in any other manner; it is the earth alone which gives them birth. Let the earth produce a living creature.
Cattle are terrestrial and bent towards the earth. Man, a celestial growth, rises superior to them as much by the mould of his bodily conformation as by the dignity of his soul. What is the form of quadrupeds? Their head is bent towards the earth and looks towards their belly, and only pursues their belly's good. Your head, O man! Is turned towards heaven; your eyes look up. When therefore you degrade yourself by the passions of the flesh, slave of your belly, and your lowest parts, you approach animals without reason and becomest like one of them. You are called to more noble cares; “seek those things which are above where Christ sits.” Raise your soul above the earth; draw from its natural conformation the rule of your conduct; fix your conversation in heaven. Your true country is the heavenly Jerusalem; your fellow citizens and your compatriots are “the first-born which are written in heaven.”
Source: Nine Homilies of Hexaemeron (New Advent)