self reliance

"Let us affront and reprimand the smooth mediocrity and squalid contentment of the times, and hurl in the face of custom, and trade, and office, the fact which is the upshot of all history, that there is a great responsible Thinker and Actor working wherever a man works; that a true man belongs to no other time or place, but is the centre of things." As Emerson say this i try to better understand but am still confused about the real meaning he is trying to get at as he tells us this?