Forget about the politcal and religious agendas!
Viva la vida means live the life! We've all heard the phrase "This is the life!" That usually implies a life of luxury and affluence, being on top, feeling powerful and important, even omnipotent, as if we ruled the world. The person speaking in this song felt on top of his game, had achieved great success in a way that he thought was "the life". He had it all, or so he thought, but he found instead, that never an honest word was spoken that it was corrupt and hollow, that he was only a lonely puppet on a string having done things to get there that severely separated him from who he truly was. However, it isn't until his castle built on pillars of sand collapses(because it isn't built on the true sustenance of the soul and can easily crumble, as it has for many in life) that he realizes this, that he comes to see it as a blessing because now he is truly free. He hears Jerusalem bells ringing, and Roman Cavalry choirs singing. These general religious references symbolize his feelings of connecting to God again, to his core and essence now that he doesn't "rule the world". He asks God to be his mirror so he can truly see himself again, his sword so he can fight for what he knows is right, his shield so he can protect himself from corruption. He lost everything, but in essence he has gained everything because he finds his soul again and now truly is "living the life". That's why he feels St. Peter will call his name and he will be forgiven. I feel the music and the lyrics convey joy and exhaltation. He is liberated. He no longer has to live a lie. Cunning business men know that competitors would want their head on a silver plate if they could manage. The lyrics are metaphorical and don't have to be taken so literally! It's just a suggestion. This is poetry and songwriting at its best. It's a phenomenal song and the music helps convey the message beautifully and brilliantly.
Songs like this don't come along every day. I loved it immediately and it gives me chills every time I hear it.
Coldplay - Viva la Vida