In my opinion, I believe he's trying to say this is what we as humans think when in war. (Since this is also played with the song "This Is War" on their album) That not necessarily he doesn't believe in those things, but that when we are in war we tend to get caught up in things, and in the end we only focus on the beating of our hearts and the truth of who we really are as humans. We sort of block everything else out, and may not focus on what we really truly believe in.
Also I think it could speak of doubts we have, we may always have doubts on certain things (ie. the earth, stars, end and start, sin and God, peace and war, etc) but we never doubt the beating of our hearts and our lives and we never doubt who we are. Because those are things we know are real no matter what.
In my opinion, I believe he's trying to say this is what we as humans think when in war. (Since this is also played with the song "This Is War" on their album) That not necessarily he doesn't believe in those things, but that when we are in war we tend to get caught up in things, and in the end we only focus on the beating of our hearts and the truth of who we really are as humans. We sort of block everything else out, and may not focus on what we really truly believe in.
Also I think it could speak of doubts we have, we may always have doubts on certain things (ie. the earth, stars, end and start, sin and God, peace and war, etc) but we never doubt the beating of our hearts and our lives and we never doubt who we are. Because those are things we know are real no matter what.
So it can be interpreted in two ways for me.