the general message of the song is that as long as you are a simply "spectator" your ideas, beliefs and convictions will mean nothing. "architects and engineers" are people who design things ("vision"), but they are not the ones who actually put in the physical labor to actually accomplish the those things. the speaker is now an "ex-spectator" or "participant" a person who takes action, working towards the accomplishment of whatever he believes in.
the general message of the song is that as long as you are a simply "spectator" your ideas, beliefs and convictions will mean nothing. "architects and engineers" are people who design things ("vision"), but they are not the ones who actually put in the physical labor to actually accomplish the those things. the speaker is now an "ex-spectator" or "participant" a person who takes action, working towards the accomplishment of whatever he believes in.