Lyric discussion by raavequeen 

Cover art for Occam's Razor lyrics by 30 Seconds to Mars

Just google "Occam's Razor" and it'll tell you what the song's about.

"Occam's razor (also written as Ockham's razor, Latin lex parsimoniae) is a principle of parsimony, economy, or succinctness used in logic and problem-solving. It states that among competing hypotheses, the one that makes the fewest assumptions should be selected.".... The razor's statement that "simpler explanations are, other things being equal, generally better than more complex ones" is amenable to empirical testing.

Basically: The simpler explanation with the most proof is the one most likely correct. Is it more likely we're all here on earth by chance and evolution (as literally all the evidence points to), or is it more likely we're here because of a super-complicated deity who's communications with people have always matched up very very closely with the beliefs and practices those peoples already had before the supposed communication, and who never shows themselves?

It's a song about how religious people blind themselves to so much of the world and it's beauty so that they can cling to their beliefs, which are much uglier.

It doesn't seem to be hateful toward religion, though, just observant, and Jared Leto's religious beliefs or lack thereof are still in question (he doesn't talk about them).

Song Meaning