An excellent episode. I like it so much!
Discord being in his own unique way the teacher more than ever, taking care of the last remnants of problematic ideas from the past that unsurprisingly Twilight would cling to the most, since she is very intellect-focused, and the mind is the origin of all suffering.
It also showed how easily one can fall into self-delusion by making up a self-image designed to avoid being honest to oneself. That kind of honesty being the crucial first step in having a positive impact on the world by having a positive impact on yourself. Thus also hinted at how when we THINK we got stuff figured out, safe and secure, that might be the most dangerous time.
And I especially liked the somewhat unspoken message in the lesson:
That true friendship comes from the heart, not the mind.
The mind on its own would attempt to create a fake of the real thing, an imitation. Something you can observe every day; best example corporate marketing, but also in individuals.
I also grinned knowingly at one point and was wondering whether the writers intended the hint at the irony:
When Twilight was at Zecora's place and insisted that there must be some kind of magic involved in her friends' behavior, I thought:
Well, DUH! There's indeed that one special kind of magic that causes people to have a great time together. You claim to be the Princess of Friendship, educated and skilled in various forms of magic. I'm quite sure you've heard of it.
By the way, Zecora's potion bottle was definitely magical, too. I mean, did you see how much liquid came out of the thing?!
You know, with stories like this, I'm not worried that they might run out of ideas and the show takes a nosedive. As long as they keep having fun like this and don't change the formula, it gives me a warm feeling when thinking about the future. With so many things in our world eventually becoming corrupted, there needs to be at least one exemplary defiant champion in our life. As long as the makers of the show heed their own lessons, we're all safe.