You may be aware that US Copyright law protects works for a certain period of time (let's say 100 years for the sake of argument). After this, the works are in the public domain. This means that anyone can publish them without paying royalties. But they still have to acknowledge the source. And whether you are using Plato, Josephus, Machiavelli, Michelangelo, Emerson, Chesterton, T.S. Eliot or e.e. cummings, you must cite your sources. If you cite a long passage in your paper, and the work is still under copyright, you will need to get the permission of the copyright holder to do it. The law is complicated here, because if you can show that your use is "fair," you may not need permission.
But let me ask you this question: what are you doing citing a long passage in the first place? It will take up so much space in your paper that there will be very little room left for you own thoughts. I have seen more than one case where students have turned in papers that were largely (and I mean almost word-for-word largely) other people's work. If the student had put quotation marks around each passage, it would have been painfully obvious that the amount of material added by the student was practically nil. So with the quotation marks and the citations, technically it's not plagiarism. But if the substance of the paper is completely missing, it should get an F from the Professor. That's still preferable to an Honor Council sanction, but is it what you came to college for?