they shall drive thee - a Chaldee idiom for “thou shalt be driven.” Hypochondriacal madness was his malady, which “drove” him under the fancy that he was a beast, to “dwell with the beasts”; Dan 4:34 proves this, “mine understanding returned.” The regency would leave him to roam in the large beast-abounding parks attached to the palace.
eat grass - that is, vegetables, or herbs in general (Gen 3:18).
they shall wet thee - that is, thou shalt be wet.
till thou know, etc. - (Psa 83:17, Psa 83:18; Jer 27:5).