John Trapp on Job 40:23

Verſe 23. Behold he drinketh up a River, and haſteth not] Viz. Through fear, tanquam canis ad Nilum, as the dogs that drink at Nilus fear the Crocodile; or as they of this Land anciently drank in fear of their lives the whiles, and were therefore wont to have ſome friend to undertake for their ſafety: whence that expreſſion of him who is drunk to, I'll pledge for you. The Elephant as he drinks huge draughts (beyond that of the Camel,Lib. 8. cap. 18. who drinketh, ſaith Pliny, Et in praeteritum, & in futurum, for both the time paſt, and the time to come) ſo he drinks without diſturbance for who dare deal with him? Other cattle, through the frightfulneſſe of their diſpoſition, break their draughts to ſtare about them. Not ſo the Elephant, who drinks as if, he would exhauſt and drain dry the River, and ſteps into it with ſuch a big body as if he would ſtop the courſe of it; therefore ſome read the words thus, He hindreth the River that is haſteth not. Some by he haſteth not, underſtand that cuſtom of the Elephant, not to drink, till he have firſt by going into, and ſtirring the water made it pudley, for he loveth not clear waters, as Elian writeth. Neither yet doth he at any time enter higher into a River then he can breath through his large Snout, for ſwim he cannot by reaſon of the weightineſſe of his body, ſaith Ariſtotle. Hiſt. anim. l. 9. cap. 46.

He truſteth that he can draw up Jordan into his mouth] In the vaſt imagination of his fancy he conceits that he can devour and drink up whole Jordan at once. Jordan is the greateſt River of Canaan, running along the Land, and falling into the dead Sea which yet grows no bigger by ſwallowing it. Hereunto ſome think, that this Text alludeth. But better by Jordan here, (which ariſeth from the root of Lybanus, and as ſome ſay, from a double fountain, the one on the right ſide called Dan, and the other on the left called Jor) we may underſtand by a Synecdoche, any River; and ſo theſe words are nothing elſe but an hyperbolical repetition of the former.