If our eyes only saw frames (IE: 30 images a second), like a single lens reflex camera, we'd see images pop in and out of existance and that would really be annoying and not as advantagous to us in our three dimensional space and bodies.
In the Vienna of the second half of the 18th century, in addition to Haydn and Mozart, three symphonic composers, namely Leopold Hoffmann, Carl Ditters von Dittersdorf and J.B. Vanhal helped further the development of the symphony.
(YouTube: Listen to Beethoven's Symphony No. 5.) The symphony as we know it today evolved from the 18th-century opera sinfonia, a style of music comprised of a fast movement, slow movement, and dance-like movement that was used in operas, suites, cantatas, and oratorios as a prelude, interlude, or postlude.