This is Prelude No. 1 from Book 1 of The Well-Tempered Clavier by J.S. Bach, which Wikipedia refers to as “generally regarded as one of the most important works in the history of classical music.” I agree, although this particular selection from the WTC’s 48 is by far the easiest, and the only one I can play. (I’m not much of a pianist.) Here’s the sheet music.
Messing around with echo, I thought it would be fun to try it at a speed matched to the echo, offset by an eighth note. Each half measure of the piece is a single chord, played as a single-line arpeggio; with the echo, this becomes a string of consonant intervals, with a bit of blurring between each chord change. It’s a fun effect!