The quotation, 'What dire offense from amorous causes springs,/What mighty contests rise from trivial things' is the opening couplet of Alexander Pope's 'The Rape of the Lock.' It is written in the voice of the narrator, and addressed to, or overheard, as it were, by, the reader of the poem. It refers to the central incident in the poem, the seizing of Belinda`s lock of hair by Lord Petre, that constitutes the main action of the poem. Its significance is that it sets the tone of the poem as a mock epic, dealing with a contest not over great kingdoms and deeds, as in serious epic, but over trivia.
For a 300-word answer, you might expand on how the introductory couplets of the mock epic relate to the traditional invocation of the Muses of actual epic, especially with reference to Pope`s Homer.