I just learned the vocabulary for please, 下さい. I was wondering if anyone knows why the kanji for below is used in it?
It’s the command form of 下さる (to give, from someone socially above the speaker). So it is being “lowered” to the recipient metaphorically.
To give to someone socially above you, you use 差し上げる (さしあげる) so you can see the opposite kanji in use.
Oh, thanks! 
great question, i wondered this too
thanks leebo for the answer 