How to understand the phrase in boldface?
The body being the only instrument that savage man is acquainted with, he employs it to different uses, of which ours, for want of practice, are incapable; and we may thank our industry for the loss of that strength and agility, which necessity obliges him to acquire. Had he a hatchet, would his hand so easily snap off from an oak so stout a branch? Had he a sling, would it dart a stone to so great a distance? Had he a ladder, would he run so nimbly up a tree? Had he a horse, would he with such swiftness shoot along the plain? Give civilized man but time to gather about him all his machines, and no doubt he will be an overmatch for the savage: but if you have a mind to see a contest still more unequal, place them naked and unarmed one opposite to the other; and you will soon discover the advantage there is in perpetually having all our forces at our disposal, in being constantly prepared against all events, and in always carrying ourselves, as it were, whole and entire about us.
-- from Rousseau's “Discourse on Inequality”