Three

The key lines in this song as I read it are "I'll give back all the knowledge / And keep the wisdom precious in my mind."

As we learn, we learn how to learn. The more knowledge we gain and the more context we have for it, the better equipped we are to find patterns, connections, and meaning underlying raw data. The catch is that by the time we've achieved this level of data processing capability our minds are full of misconceptions, biases, and knowledge which was uncritically assimilated.

There is, then, a desire to keep the mechanism of the trained mind intact, while stripping it of so much useless knowledge. Presumably, one could then relearn everything using a "better" brain.

At the same time, our knowledge, inaccurate as it may be, is something that is significant in helping us define ourselves. To simply erase all of that is a frightening prospect from the standpoint of identity.

And finally, there is the titular number three and its meaning to the song. Children, lacking both knowledge, intuit something special about the number three, but they lack the processing experience to examine that intuition. If a person could combine the mental reasoning of a lifetime of thinking (unadulterated by knowledge) with the natural intuition of a child, one might be able to discover fascinating things about the nature of reasoning, experience, or something else.

i love this song so much that i dont wanna make any comment on it....i dont wanna spoil it :) leave it as is...

:) one of my all time favourittes...

I think it's about missing the times you were inexperienced, because you will never get the feeling of learning for the first time again. That's the thrill of life.

Mind, though, that nobody ever stops learning... :)