What, but education, has advanced us beyond the condition of our indigenous neighbours? and what chains them to their present state of barbarism & wretchedness, but a besotted veneration for the supposed supe[r]lative wisdom of their fathers and the preposterous idea that they are to look backward for better things and not forward, longing, as it should seem, to return to the days of eating acorns and roots rather than indulge in the degeneracies of civilization.
This sentence is trying to show how important education is, and they did so with a rather cruel example.It is saying that without education, we would just be like the Native Indians, which are "barbaric", "wretched", and just wants to eat acorns and roots all day. Without education, it is sticking to the past. With education, we look forward into the future.