It sounds like you're looking at , titled "For Everyone's Sake" (みんなのために). This is a heavy-hitting chapter right in the middle of the "Promised Day" climax.

I look at Al—or what’s left of him in this hollow suit—and I see the price we paid. Now, the sky is turning dark, and the 'Father' of all shadows thinks he can swallow the sun. He thinks he can turn millions of souls into a stone just to fill the hole in his own chest.

Here is a short creative piece—a "monologue of resolve"—inspired by the events and themes of that specific chapter: The Weight of the Soul

"We aren't gods. We aren't even heroes. We’re just two brothers who learned the hard way that the world doesn’t give you anything for free.

If you’re looking to read the chapter or find more info, you can check out the official Fullmetal Alchemist page on Viz Media or the fan-led FMA Wiki.

But he’s wrong about one thing. He thinks a soul is just fuel. He doesn’t see the spark in the people standing behind me. He doesn't see the Colonel’s burnt eyes, or Winry’s wait, or the soldiers who refuse to die.