Is the essay supposed to be based on quotation, or merely inspired by it. It makes a difference. In any event, you could try one of the following:
"The last temptation is the greatest treason: to do the right deed for the wrong reason" (T.S. Eliot)
"Things fall apart; the center cannot hold;" (Yeats)
"Death closes all: but something ere the end, / Some work of noble note, may yet be done / not unbecoming men who strove with gods" (Tennyson)
"Not only does God play dice with the Universe - he sometimes casts them where they can't be seen" Stephen Hawking
Sean, EssayForum.com