In the course of this chapter, you will see how Western classical music evolved

In the course of this chapter, you will see how Western classical music evolved from monophonic chant to more complex four-voice polyphony. To get a feeling for the music of the Middle Ages, listen to the opening of an early fifteenth-century Requiem Mass (Mass for the Dead).
 https://youtu.be/kcRku6UL9YQ?list=PLC8C8303D7E9A6B38 
As you listen, ask yourself the following questions: Can I understand the Latin text? Even if I can’t understand it, does this lessen how I feel about these sounds? 
Similarly, do you find this music from 600 years ago any less beautiful than that of today? Judging from this one musical example, have humans gone forward, backward, or sideways?