A symphony is divided into four movements; the first movement is usually fast, the second one is slow, the third is medium, and the fourth movement is fast. This pace is intended to keep the listener invested and interested in the progression of the music.
The four symphony movements are classified according to rhythm, key, tempo and harmonization. They include an opening sonata or allegro, a slow movement called adagio, a minuet with trio, and an allegro, sonata or rondo.
A symphony typically tells a story. It's structured like this to create a narrative arc with an attractive, interesting beginning and a slower, romantic mid section that's followed by a medium part that brings story to its peak and leads to a fast ending.