For being patriot.
It's one of the most famous Polish patriotic poems. Now we just need to learn a tiny part, but in the times of Poland being conquered by other countries in XIX century, and during German occupation during II WW, most people were learning this out of their own will.
Full recitation takes about ten minutes.
This is famous scene, in which Polish student recites it to teacher in Russian school, knowing that everybody in class can be punished for that. But what he said is only part, not to make the scene to long.
http://www.youtube.com/watch?v=O3efQ8yXmFg
I can't imaging memorising that.