Decoding the Lyrics

'Believer' by Imagine Dragons

Dan Reynolds, lead singer of Imagine Dragons made a documentary called "Believer" that is about LGBT+ rights and such. Since Imagine Dragons have a song with the same name, I'd believe they have the same meanings. Since Dan Reynolds himself is not gay, I think the song would be sung from the point of view of a struggling gay member of society. There is repeated lyrics, I will only do my explanation for the lyrics once for each different lyric. Be sure to read the WHOLE thing, at the end their will be a word from whoever had thought/decoded the meanings of this song and facts that add on to the reasoning/evidence of our thoughts and for sources.

"First things first, I'ma say all the words inside my head" would mean that they (the person who's point of view we are hearing) is saying they are tired of hiding their sexuality, and want to finally say what they have wanted to say about themselves for a while.
"I'm fired up and tired of the way things have been" means they are tired of all the homophobic beliefs they have to hear from the people around them and in society.
"Second things second, don't tell me what you think that I should be. I'm the one at the sail, the master of my sea" would be that they are done with being labeled as heterosexual (straight) and that they are in control of what they are to be called.

"I was broken from a young age" probably means they were told being gay was strictly forbidden and was a heavy sin to bare, and were possibly punished if they were to get caught saying or doing 'gay things'.
"Taking my sulking to the masses" could mean they were continuously growing their silent annoyance of homophobia. Sulking means to 'be silent, morose, and bad-tempered out of annoyance or disappointment' [source: Urban Dictionary {1}]. Or, they could of been continuously being silent about being gay.
"Write down my poems for the few that looked at me, took to me, shook to me" means they would try to communicate to those who understood that he was afraid or that he was gay. If the song's setting was around our time, the lyric could of meant that they had secret social media accounts that no one they know personally knew about, and would discuss their fears and ask for information or directory about homosexuality with people on those social media accounts.
"Feeling me singing from heartache from the pain, taking my message from the veins" would mean they would let out their feelings and fears to those they trusted, or, as explained for the last lyric, people on social media.
"Speaking my lesson from the brain" means they would take the information that they know from what the people around them taught them and learn more or make the information correct. Or, this could mean they decided to defend the gay community, possibly could have finally snapped at friends or family that were judging gays aloud.
"Seeing the beauty through the (skipping past the "you made me a believer, you made me a believer" part) pain" possibly could mean they know the consequences of telling society that they are homosexual, but have decided that the beauty (possibly the pride) of who they are is worth the consequences.
Now, going back to the part I skipped ("you made me a believer, you made me a believer"), I believe that would mean they are saying it in a angry way, like accusing someone of making them believe homosexuality is a sin. Or, it could mean they are talking about the people who showed them the truth and that being gay is okay.
"You break me down, you build me up" could mean that they are talking about two different sides, the society of homophobia they grew up in, and the society that helped them understand what being gay is and accepted them. The homophobia society is the one breaking them down, telling them they are a disappointment and are a sinner. The accepting society is the one helping them back up from being beaten down by the homophobic society, both beaten verbally and physically.
"Oh let the bullets fly, oh let them rain" means they are not afraid of the hate, and will accept death if someone where to kill them out of hate.
"My life, my love, my drive came from pain" I would believe means their new beliefs, pride, and excitement came from past pain of being scared of being disowned or hated. They have put the pain behind, and their life, love, and drive (beliefs, pride, and excitement) and have grown upon the foundation left behind by it (the pain).