A central concept in Emerson's theories of unity, on which he expounds at great length in "History," is that all historical figures—great and terrible—are reflections of the same human mind at work. Given that it's this very same human mind that the reader will be using to peruse Emerson's writing, Emerson argues for a vision of history that treats every historical figure as a version of our own selves—which means that we can learn from historical mistakes as if they were our own blunders.
This much he relates through the use of allusion and simile:
Each new law and political movement has a meaning for you. Stand before each of its tablets and say, 'Under this mask did my Proteus nature hide itself.' This remedies the defect of our too great nearness to ourselves. This throws our actions into perspective,—and as crabs, goats, scorpions, the balance and the waterpot lose their meanness when hung as signs in the zodiac, so I can see my own vices without heat in the distant persons of Solomon, Alcibiades, and Catiline.
Emerson compares the way that the zodiac neuters and distills the wild nature of animals by adopting them into the zodiac signs with the way that our own vices soften if we consider their historical counterparts in famous figures of the past. He grounds the simile in an allusion to a few famously divisive biblical and classical figures: King Solomon, a king of Israel in the Old Testament who lived a life of self-indulgence and sin, Alcibiades, a treacherous Ancient Greek statesman who played both sides in the Peloponnesian War between Athens and Sparta, and Catiline, a Roman politician who led a failed coup against the Roman government.
From Emerson's perspective, we can use the study of history—the study of our forebears and their own flawed human nature—as a path toward productive, self-critical reflection.
To Emerson, each everyday experience—even the most mundane—is microcosmic for much larger natural, historical, or cosmic events. At one moment, Emerson uses a small but elegant simile in service of this philosophy, comparing the moonlight that bursts through the clouds at nighttime with the light from the the creation of the universe:
The man who has seen the rising moon break out of the clouds at midnight, has been present like an archangel at the creation of light and of the world.
Emerson's argument for the significance of individual experience—and the importance of individual subjectivity—hinges upon this very kind of correlation. If men and archangels are not so dissimilar, if moonlight shining out of the clouds on a clear night has the very same grandeur and universal significance as the very first light shining out at the moment of creation, then the human mind has no limit to its powers of comprehension. Humans, Emerson argues, can appreciate each other—and all of nature (or "creation")—as if they were appreciating themselves, because everything is cut from the same fundamental cloth.
This passage is also an excellent example of how Emerson's philosophy draws influence from Christian faith. When he references cosmic events like the creation of the universe, he couches them in biblical language—in this case, in the language of the Book of Genesis that recounts the Judeo-Christian Creation story.