...There's no way to, really.
I mean, I could try. I could try to communicate what this fic is. And I might get close. But then, I probably wouldn't actually get there.
Yes, it's that kind of story. The kind that defies explanation. The kind that hits so deeply on an emotional level that words - other than the words of the fic itself, of course - just don't cut it.
All I can really do is give this fic my highest recommendation. The ideas are simple but engaging; the execution is nigh-on flawless. It strikes that perfect balance between complexity and simplicity, and while in theory it would take very little thought to follow the story you find yourself drawn into focusing on it with total concentration.
It is not a fic for everyone. If you are looking for an epic adventure, you will not find it here. If you are expecting shipping and friendshipping and heaps of adorable ponies, you will be disappointed. And if you are looking for something sunny and bright and ubiquitously happy, you are looking in the wrong place.
But if you think you will enjoy something cerebral, touching, and ultimately inspiring, then you have found the right fic. And even if you don't...you should give it a shot anyway.