Thou wilt surely wear away,.... His natural strength and animal spirits, and so his flesh; he feared his constant application and attendance to business would impair his health, break his constitution, and bring him into a consumption.
Moses was naturally of a strong and vigorous constitution; for, forty years after this, even to the time of his death, his natural force was not abated; or "fading thou wilt fade", or, "falling thou wilt fall" ; in allusion to the leaves of trees in autumn, which fade, and wither, and fall:both thou and this people that is with thee; it was tiresome to the people, as well as fatiguing to Moses, who, because of the multitude of cases, were obliged to wait a long time, some of them from morning to night, and yet could not get their suit to come and so were obliged to attend next day, and perhaps day after day.
The Targum of Jonathan is,"even thou also, Aaron and his sons, and the elders that are with them;''and so Jarchi; but these do not seem to have been assisting to him at all, as appears by what follows:for this thing is too heavy for thee: it was too great a burden upon his shoulders, what his strength was not equal to; for though his internal abilities were exceeding great, and he had a good will to the work, to serve God and his people, yet it was more, humanly speaking, than his bodily strength would admit of, or any mortal man could go through:thou art not able to perform it thyself alone; and this Moses was sensible of himself afterwards, and says the same thing, De 1:9.