The moral of the episode seems to be 'Celestia is Dumb'. Really, really dumb. Twilight, who wants to be useful and hates being seen as a princess, is called to the Crystal Empire to smile and wave while being cut out of the important discussion.
"So, if you're the princess of the sun, and you're the princess of the moon, and you're the protector of the Crystal Empire, what do I do?"
"You just haven't earned it yet, baby. You must suffer and cry for slightly longer."
No, wait, they sang their own song, which was okay but really just told her to stop whining and eventually she'd figure it out.
Then Tirek escapes. "We need to strike while he's still weak! Let's send Twilight!" "No, this is a job for Discord." "... what?" "He can sense where Tirek uses his magic and track him down instantly." "Okay. Let's send Discord *and* Twilight?" "No. Just Discord. I trust him completely."
...the actual discussion in the episode was shorter. It still lasted longer than Discord's loyalty in the face of vague promises of power.
Then there was the plan to give all the alicorn magic in Equestria to Twilight so that she could... do... something. Certainly not fight Tirek. There wasn't really any plan to fight Tirek. Once Discord turned on them, Celestia basically gave up. I think Twilight was just supposed to hide until Tirek went away, and then give the magic back.
Unfortunately, Discord knew that Twilight existed and how to find her. Everypony knew that he knew. Everypony knew that he was working with Tirek. What the FUCK, Celestia? I think somebody from Fimfic (RainbowDoubleDash?) put it best: "This plan is dumb. You're dumb."
So, the moral of the story is that Celestia is dumb, and Twilight Sparkle will do literally anything that Celestia asks her to, including give up her magic and DOOM EQUESTRIA by sending Discord off after Tirek alone.
But if you set fire to her books, she will kick your tail. With lasers. Lasers made of pure antimatter.
Also, Tirek has an irrational hatred of trees. Or maybe overcharging him with all the magic ever made him crazy? Because after getting ultimate power, he immediately started blowing up trees with a laser beam for no apparent reason. He wasn't searching the forest for ponies hiding in it or anything -- he knew where his enemies were because he left them drained at his hooves to go off and blow up trees instead.
"Okay! We've said the words! Discord learned a valuable lesson about friendship after I made a difficult decision involving my element, and then he gave me a trinket! So... I'm inserting the key now."
The fact that both Discord and Twilight knew what was going on and were consciously going through the motions make the previous scene a little more bearable. You know, where she gives Tirek, a crazy liar who'd just betrayed Discord, ultimate power in exchange for her friends. Because he's totally going to uphold his side of the bargain and won't just snap his fingers and put them all in bubbles again.
Of course he won't. There are trees to destroy.
Still... it was a pretty good pair of episodes. Except for the castle at the end, that's just tacky. 2/3.