Lyric discussion by jamzb 

Cover art for Be Concerned lyrics by Twenty One Pilots

I think he is talking about doubt in God. He references the Bible a few times "Jonah" and "You are the pearl, I am the swine" are the main examples.

He is saying to be concerned because he fools everyone into thinking that he has this strong faith "Sorry Mr. Gullibe", but he is on the edge of being done with his faith.

He goes through some reasons involved in this: to devote a single inch to something i can't see. But with the reasons there are some feelings of it "I'm scared of my own head" "you are the pearls, I am the swine" That last quote I think refers to either his reasoning of help me cause I'm the swine, or of I am sorry I doubted because you are a pearl and I am a swine.

Song Meaning