His tail sways like a cedar; the sinews of his thighs are tightly knit.
God, for the further proving of his own power and disproving of Job's pretensions, concludes his discourse with the description of two vast and mighty animals, far exceeding man in bulk and strength, one he calls behemoth, the other leviathan. In these verses we have the former described.
Commenting on Job 40:15-24
His bones are as strong pieces of brass: his bones are as bars of iron. Than which nothing is stronger. The repetition is made for greater illustration and confirmation; but what is said is not applicable to the elephant, whose bones are porous and rimous, light and spongy for the most part, as appears from the osteology (k) of it; excepting its teeth, which are...
like a cedar--As the tempest bends the cedar, so it can move its smooth thick tail [UMBREIT]. But the cedar implies straightness and length, such as do not apply to the river horse's short tail, but perhaps to an extinct species of animal (see on Job 40:15). stones--rather, "thighs." wrapped--firmly twisted together, like a thick rope.