Colorful, well-chosen quotes can infuse an essay with energy and vitality, so you're smart to use them. But when a quote gets too long, it's time to set it apart. Do so following the documentation style recommended by your teacher -- most likely American Psychological Association or Modern Language Association style.
APA, which sets style rules for papers written in the field of social science, refers to quotes with more than 40 words as a block quotation. Start the quote on a new line, indenting the quote ½ inch from the left margin; you do not have to indent the right margin. Double-space the quotation, end it with a period and then include the citation information. By setting off the quote in this manner, you do not have to enclose it in quotation marks.
MLA, which sets style for papers written in the field of the arts and humanities, calls a long quote that consists of more than four lines of prose or three lines of verse just that: a long quotation. Omit quotation marks as you begin the quote on a new line, indenting it 1 inch from the left margin; you do not have to indent the right margin. Double-space the quotation, place a period at the end and then include the citation information. If you are quoting multiple paragraphs, indent only the first line by an extra ¼ inch.
Show Regard for the Reader
Quotes can speak volumes, but only if your reader knows who's talking and understands the context. Preface your quote with enough information so that it makes sense and the reader can appreciate it. For example, you might say, “Hemingway understands how real people argue, as he shows in a confrontation between Jake Barnes and Lady Brett Ashley in The Sun Also Rises:” -- before you break out the long quote.