materialism
Rousseau is making the paradoxical point here that to begin a spiritual education with abstractions ends up by establishing materialism (i.e. the belief that ultimate reality consists only of matter, the "hard" objects of the external world). He may have been suggesting that while Locke's educational writings recognized spiritual themes, his Essay Concerning Human Understanding established the basis for modern empiricism and materialism. Rousseau's approach will be very different. In the "Profession of Faith of the Savoyard Vicar" which follows, the close observation of empirical reality will lead the observer to an appreciation for a higher spiritual power.