Let's see... Why do I love Celestia and Luna more than anypony? Well first off, they both were the first MLP characters I discovered and the reason I became a fan in the first place. All it took to turn me was a video about Princesses and of course at first, I didn't think much of it because I thought it was simply just another girly show to avoid, but one day I actually took a chance and looked up pictures of Celestia and Luna and went and looked on the wikia for more information, only to discover how incredibly powerful and very beautiful they both were. One rose the sun and the other rose the moon? That's amazing. Even before MLP, I always had a thing for Princesses in the past, and being a Legend of Zelda and Sonic fan, it was easy for me to fall into the love for these two princesses.
So, I actually took my chance a step further and watched an episode of the show that was about the princesses and "A Royal Problem" was the first episode I watched. At the time, I didn't know who Twilight or Starlight was and just watched the two princesses scenes instead. Both Celestia and Luna were hilarious in the episode and it got a good laugh out of me at one point.
3 years of being a MLP fan later, I questioned myself again: Why do I love these two beautiful alicorn princesses so much? And the only answer I can give is because they both taught me a valuable lesson of how to forgive and forget things that happen in the past. After going back and hearing of the whole Nightmare Moon thing that happened to Luna, something born out of a misplaced jealousy and the poisonous ways Luna tried to make her own sister suffer, it actually made me sad to hear that she was banished to the MOON for a thousand years for her actions. But of course, this was because Celestia had no other choice, or else Luna's rage at her sister would have turned to the newborn kingdom they both had the responsibility of holding together. Celestia was indeed broken from this battle, wondering to herself if she would ever see her dear sister again or if what she did to Luna was wrong, every time she looked toward the Moon where Luna then resided.
A thousand years later, Twilight and her friends save Luna from her torment and what does Celestia immediately do? Not scream or yell at her for what she's gone through for the past thousand years, but instead embraces her sister and asks for her friendship and sisterhood once more, with Luna happily agreeing to and begging for Celestia's forgiveness, unaware that she already had forgiven her.
They're sisters, and that all that matters. Never mind all that happened in the past, let it stay there, because the only thing that matters is what you choose to be in the future. As long as you or someone you know is willing to let go of the past, you can make it through anything, no matter how hard or tough the situation is!
I can think of no better teachers than the two Royal Sisters. Both are so beautiful and incredible and even after a thousand years apart from one another, they're both still sisters until the end!