The intent and emotions of the composer, what he was feeling, as he wrote it. It's about unrequited love (Quasi Una Fantasia). The first movement is the most popular, but if you have 15 minutes or so listen to the whole thing. Beethoven was incredibly shy by all accounts, and the only way to express himself was through his compositions. It's sad, gloomy, and ferocious. Roy Buchanan was a lot like him. Shy, introverted, not physically attractive. His Messiah Will Come Again is in many ways just like a classical sonata. Starts out slow, builds up tension, then explodes. Sad, gloomy, and ferocious. You don't need words to convey sadness, loss... the things you felt are left unfulfilled. You can convey all of these things and more simply though the music. It's why it is the universal language. We all can get it.