Well im only 16 here, but my parents went through a divorce, and i think i can kinda relate to this song. I'm thinkin its about john fogerty's father leaving him and telling him that "Someday you'll understand". Yet that day never came, and he eventually did the same thing, and he sings about leaving his son, telling him "Someday you'll understand." All the while he's singin in the chorus speaking to the 'mother's song', which would be people that were raised by their mother, and never really had a father. He's telling those people that you need to learn it on your own, and hopefully 'break the cycle'. So that you don't do the same to your kids. So I'm thinkin its about Divorce and how important it is to have a father.

let me know if you think this is a pretty good explination...

-eilert