Interpretation of Green day's song "21 guns"

Summary

The song is about fighting a good fight, but not the fights unworthy of fighting for. You only got one life, and just one 21 gun salute, avail of it. Live your life an honorable life and give up the petty things.

You should know what/who you are living for. Live for yourself. If you're living for someone else, what will happen to you if that person leaves you? And you can't run to your family and friends anymore because they've already warned you of that predicament, and running to them would only mean eating your pride and proving them right. You'll just be alone. And all you'd be are ruins. Ruins of what you and your significant other used to be.

I

"Do you know what's worth fighting for,
When it's not worth dying for?
Does it take your breath away
And you feel yourself suffocating?"

Verse I asks if you're giving importance to the right things, or are you just wasting time. And those unimportant things which are not worth dying for are the one's that mosts kills/suffocates/takes your breath away.

II

"Does the pain weigh out the pride?
And you look for a place to hide?
Did someone break your heart inside?
You're in ruins"

(Line 1,2) Are you willing to endure the pain alone and hide yourself from others, just because you're too proud to seek help?

(Line 3,4) Did you lost someone important, because you look so devastated(ruins).

III
"One, 21 guns
Lay down your arms
Give up the fight
One, 21 guns
Throw up your arms into the sky,
You and I"

Verse III says that you only got one life, and if you use your life fighting for the worthy things to fight for, then you are worthy of a 21 gun salute/an honorable death. One life, one death. One life put to good use, one 21 gun salute. It also tells that when the bad times overshadows the good times, you should learn to let your guards down to allow someone(a friend) to come in to your life and to comfort you.

IV

"When you're at the end of the road
And you lost all sense of control
And your thoughts have taken their toll
When your mind breaks the spirit of your soul
Your faith walks on broken glass
And the hangover doesn't pass
Nothing's ever built to last
You're in ruins"

(Line 1,2) When you feel like all the bad things are getting worst, and you don't have control of the things. You don't know how to make things better.

(Line 3,4) You mind is bothered by all the things that are happening, and you think that you can't make it.

(Line 5,6) Your faith is weakening as it walks on broken glass and your mind keeps on telling you that you can't continue.

(Line 7,8) Your mind is telling you that you can't make it. You may be strong now, but sooner or later, you're bound to give up(nothing's ever built to last). Just look at you now, you look devastated(you're in ruins).

V

"Did you try to live on your own
When you burned down the house and home?
Did you stand too close to the fire?
Like a liar looking for forgiveness from a stone
When it's time to live and let die
And you can't get another try
Something inside this heart has died
You're in ruins"

(Line 1,2) Do you feel like you've lost all the people(house and home) who loves you? Those people who you run to when your down. And now that you feel they're all gone, you try to fix yourself on your own.

(Line 3,4) Did you burn yourself from all that playing with fire? Did you get hurt just because you were trying to live your life? Are you waiting for something/someone that's so impossible that you're bound to get hurt in the end.

(Line 5,6,7) When time comes that you allow yourself to be happy(live) and let go of the things that are pulling you down(let die), but you can't. You try but you just can't. And you feel like a part of you just died(pride, maybe).