I don't know exactly what this song means but it's obviously a song about Jesus, or a being that is above us. It's already evident in some of ismfof's other songs that they don't believe in God or that they at least don't believe in the same God that Christian's do. It sounds like this song is asking, "Does God (Jesus) really exist?"
"Have you ever heard a thunder bolt voice your name?"
That lyric questions a Christian's beliefs, or their faith. No one has really ever truly seen their God, so ismfof asks this question.
"Lets all just reach our hands into the dark,.
And feel what reaches back! "
This lyric focuses more of the faith part. Faith is believing in something that you can't see and ismfof is sort of making for (or questioning) faith in general. Essentially, faith really is reaching into the darkness and feeling what reaches back.
The most obvious thing is of course the name of the song. Wtfwjd, meaning "What the fuck would Jesus do?"