It's a bit of a nod to Joe Strummer(the Clash) and what a huge impact the clash had on the very young impressionable U2 after seeing them perform live.
Soldier Soldier we signed our lives away, complete surrender, the only weapon we know-- and the bit about "Old man knows how to cheat ambition--you don't lose if you don't play". Bono always complaining that his Dad never encouraged him to dream, because if you don't dream, you can't fail, if you can't fail, you can't get hurt. So my take is it's about them choosing a life in music having a chance to say something meaningful and be heard in the world.