What is the role and function of a poet according to Emerson's essay, "The Poet"?

The poet, according to Emerson, has to be just about everything. 

He has to be a seer into the soul of man, he must be an interpreter and a prophet.

 I know not how it is that we need an interpreter; but the great majority of men seem to be minors, who have not yet come into possession of their own, or mutes, who cannot report the conversation they have had with nature. 

Mankind may see things about them in their world, but so very few ever put into words a great expression that impacts, that influences, that makes value of the every day mundane to all other men. This is the power of a poet that interprets.

The poet must be a foreteller, a prophet:

The sign and credentials of the poet are, that he announces that which no man foretold. He is the true and only doctor; he knows and tells; he is the only teller of news, for he was present and privy to the appearance which he describes.

The poet must have the ability to color and accompany life. This is the difference between watching television in black and white or on an HD LCD screen in living color. This is the difference between a tinny cheap radio and a live orchestra.

We hear, through all the varied music, the ground-tone of conventional life. Our poets are men of talents who sing.

Poets must have imagination, and they must have energy.

What are Emerson's ideas about the nature and functions of "The Poet"?

Concerning Emerson's views on the poet's nature and function, I can give you only a limited answer, but since no one else has answered yet, I'll give you what I can.

Looking at two specific poems, insight into Emerson's views can be inferred.

First, in "Ulysses," the subject of the poem is conveyed as a kind of artist.  And Ulysses, the adventurer/artist, must perform his art.  He cannot be happy as a king/administrator.  His lot in life is to travel, to be on the ocean, to perform his art.  Happiness, for Ulysses, cannot be found in Ithaca.

In Emerson's "The Lady of Shallot," the artist, it seems, must not completely separate herself from reality.  The Lady, cursed to never look upon reality, but only to interpret reality through a mirror, dies when she does so.  She is not allowed to look upon the actual Camelot.  Why?  Possibly because Camelot as she knows it does not exist.  She knows Camelot only through a mirror and through her art.  Tennyson seems to be suggesting that an artist should be careful of separating him or herself too much from reality.  If one is to reflect reality, one must know and be a part of it. 

Again, limited as my answer is, in these two poems Tennyson suggests that an artist cannot be separated from his or her art, but at the same time must be in touch with and be a part of reality.