I can't. Too feels. Not enough emotions available for processing.
Also, this doesn't seem to have really been brought up much in the wake of this last episode - which surprises me, seeing as it concerns Luna:
You see this? This is Celestia. Getting a letter. And showing it to Luna. This is not Luna looking over Celly's shoulder at the letter, this is Celestia saying "Hey, Luna, you wanna actually look at this letter sent to us, since we're equals and not everything is just sent to me in particular?"
I would've thought it would get more attention - but then again, given everything else that happened in this episode, I can't really blame anyone.
Also, AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA CUTIE MARKS