Charles Ellicott Commentary Job 40:15

"Behold now, behemoth, which I made as well as thee; He eateth grass as an ox." — Job 40:15 (ASV)

Behemoth. —The identification of behemoth has always been a great difficulty for commentators. The word in Hebrew is actually the natural plural of behçmâh, which means domestic cattle; and this fact would suggest that more than one animal may be meant in the description (Job 40:15–24), which hardly seems to apply to one and the same creature. In this way, Job 40:15–20 would describe the elephant very well, and Job 40:21-24 the hippopotamus.

The objection to this is that behçmâh is commonly used for domestic cattle in contrast to wild beasts, whereas neither the elephant nor the hippopotamus can be classified as domestic animals. There is a word in Coptic (p-ehe-emmou, meaning water-ox), used for the hippopotamus, which may, perhaps, be concealed in the word behemoth. Then the difficulty is to make the description apply in its entirety to the hippopotamus (e.g.,Job 40:20), since the hippopotamus does not frequent mountains, nor does it exactly eat grass like an ox (Job 40:15).

Which I made with you. —Your fellow creatures, made to inhabit the world with you: thus skillfully reminding him that he shared a common origin with the beasts.