Kanon Pokajanen is a really long and special song that was written by a man named Arvo Pärt. It's called "kanon" because it's like a big, long prayer that is made up of smaller prayers all put together.
The words of Kanon Pokajanen are very old and special because they come from the Eastern Orthodox Church. These words were written a long time ago to help people say sorry for the things they did wrong and to ask for forgiveness.
Kanon Pokajanen is not like most songs you hear on the radio because it doesn't have a beat or a lot of different instruments playing all at once. Instead, it's made up of only voices singing together.
The people who sing Kanon Pokajanen have to practice a lot because it's very hard to sing. They have to make sure they are all singing together and with the same feelings, so they can make it sound really nice.
When people listen to Kanon Pokajanen, they might feel peaceful or calm because it's like listening to a big prayer being sung all at once.