Through the works of the poets, the common person can come to better understand the world of symbols that he lives in. The common person cannot understand the world without the poet, but Emerson does not look down on them for that. It does not matter that he cannot understand the world, if he at least learns to appreciate it. This lack of understanding is why he must use symbols. He does not know the truth of what something is so he uses symbols to try to understand it and to be able to communicate about it.
Symbols are the only link that the common person has to the world.
This link is so strong that many people take the symbols to be that which is real rather than just a representation of the real thing. Since symbols are used by everyone, they need to be universal. Although there are many different languages in the world the meaning of their words are still the same. A tree is a tree is a tree. No matter how you pronounce the word tree in English, French, or German, the tree will never be a sink.