Reveal the importance of the essay by linking back to the introduction. For instance, if you began the essay with an anecdote, end it with the same anecdote in a different light to give credence to the helpfulness or insight of the essay.
Give the essay a sense of completeness by tidying up the claims of your essay. Avoid introducing new claims, as it is too late in the essay to do so and will leave your readers feeling unfulfilled.
Impress upon the reader a sense of a challenge, insight or foresight. Use strategies such as calling the audience to action, appealing to logic or emotion and stressing civic or human responsibilities. Such techniques give the reader a reason to think about your essay long after the last word has been read.
Synthesize the essay instead of merely summarizing it. Inform the reader how the sum of your points are worthwhile and useful in reality. Only use repetition as a means to an end, a tool to invoke a certain sense related to the essay.