To begin, one must be able to identify an imperative sentence. An imperative sentence is one which gives advice or expresses a request.
Paragraph thirteen of Emerson's Education, written by Ralph Waldo Emerson, is as follows:
Whilst thus the world exists for the mind; whilst thus the man is ever invited inward into shining realms of knowledge and power by the shows of the world, which interpret to him the infinitude of his own consciousness--it becomes the office of a just education to awaken him to the knowledge of this fact.
Paragraph thirteen contains only one sentence. Therefore, the only sentence which can be considered an imperative one is the entire "paragraph" itself. This sentence is an imperative one based upon the fact that Emerson is offering his advice about a man's consciousness and is asking man to consider certain something. He is asking readers to consider one fact: that while the "world" exists in the mind of a single man, a man must continue to search for his own knowledge. By doing this, his own knowledge can become fact.