March 21 is the birthday of J. S. Bach, who is right up there in most lists of "most important composers." Bach was born in Eisenach, Germany, in 1685. In checking the Wikipedia article on him, I discovered that there are several sound files of his music that are part of the article. (Bach's compositions, of course, are now public domain. Individual performances may not be. The clips in the article are freely usable.)
Bach was a Lutheran. Most of his music was written to be performed in church. There are a number of web pages dealing with his religious beliefs, and how they affected his art, or listening to it. Here's a one-paragraph statement on this matter. Mark Galli, of Christianity Today, went so far as to call him the Fifth Evangelist.
The Wikipedia uses, for this article, a sound file format I had not seen before, with the .ogg extension. In checking, I discovered that this format has an open source player (Which is why the Wikipedia, an open source encyclopedia, uses it). Other articles in the Wikipedia, including at least the ones on Mozart and Vivaldi, also use this file format. I have no ability, nor wish, to tweak a media player, and you probably don't, either, but the player, for Windows, Unix, and Macintosh operating systems, is available here. (Well, sort of. There is a link from that page to this one, which has a downloadable filter for Windows Media Player. I downloaded that. Then, when I opened an .ogg file from the Wikipedia article on Bach, I had to open it with the Other option, so as to change the program I wanted to open the file with. I browsed to the Windows Media Player, which was in the folder of the same name, in the C: \Program Files folder. Got all that? After that, my computer was "smart" enough to open an .ogg file with WMP without prompting.)
Warning: Like other music files, some of the .ogg files linked to the Wikipedia article on Bach are a few megabytes in size.
There are other sources, besides the Wikipedia, that provide .ogg files. Here's a link to some of them. I haven't explored any of these, and probably won't, as most of them seem to be current popular music, which (sorry) I have little interest in.* * * * *
Added later: The Wikipedia article on Beethoven includes the entire 5th Symphony, the "Moonlight Sonata," and the 1st movement of his 4th piano concerto, a real treasure! The Handel article includes "And the glory of the Lord," "For unto us a child is born" and "Hallelujah" from Messiah. There are, no doubt, other treasures available.