By strong I mean causing some reaction on the reader (not necessarily goosebumps, maybe just a small wow).
I'm having this problem right now. Example (the bolded part):
"He told me about how squirrels collect and store nuts for the winter. Nothing unusual. What's interesting is that sometimes they forget where they bury them. Cute, but odd if you think about it. Like, why did nature give a flawed skill to an animal? Why waste its time? The answer is that nature creates imperfect creatures. And that's because--sorry, do you know how natural selection works?"
[The character gives the protagonist a metaphoric explanation about natural selection]
I mulled this over. I'd never thought about nature that way. Imperfection. Was that the reason allergies, cancers, syndromes, and other genetic disorders existed? How about death?
"But that's a very depressive thought," I said. "That means organisms are just broken machines. Including us."
"Maybe," Cath admitted. "De-Shi didn't see it that way, though. On the contrary, he found it incredible how squirrels were planting all these trees, and doing it without even knowing it. How they were rebuilding parks, woodlands, forests, jungles--home of countless plants, insects, and animals. How they were taking part in something immensely big: protecting the Earth, a planet belonging to a solar system, to a galaxy, to a vast and ever-expanding universe. All because of a tiny defect. All because an innocent mistake from nature.
"I'm not sure why, but after De-Shi finished his monologue, I felt fresh, renewed. I not only saw nature differently, but my own life as well. True, I was imperfect, and I would probably always live in pain. However, that didn't make my existence worthless; there was still space for amazing things to happen. For the sun to shine in. For trees and beautiful forests to grow.
Like, in this case, what would make the bolded part stronger? Making it longer? Adding short sentences? Or using a different choice of words, perhaps?
This is something that I consider to be strong. And it's very similar to my passage. It's from the movie Adaptation:
Point is, what's so wonderful is that every one of these flowers has a specific relationship with the insect that pollinates it. There's a certain orchid look exactly like a certain insect so the insect is drawn to this flower, its double, its soul mate, and wants nothing more than to make love to it. And after the insect flies off, spots another soul-mate flower and makes love to it, thus pollinating it. And neither the flower nor the insect will ever understand the significance of their lovemaking. I mean, how could they know that because of their little dance the world lives? But it does. By simply doing what they're designed to do, something large and magnificent happens. In this sense they show us how to live - how the only barometer you have is your heart. How, when you spot your flower, you can't let anything get in your way.