The lyrics to this song are a bit puzzling, so I'll try to interpret some of the lyrics.
I used to rule the world
Seas would rise when I gave the word
Now in the morning I sleep alone
Sweep the streets I used to own
The writer was telling about a king with enormous power, and everybody would do as he say ("seas would rise when I gave the word"). Now he is a beggar or someone poor.
I used to roll the dice
Feel the fear in my enemy's eyes
Listen as the crowd would sing
"Now the old king's dead, long live the king"
The king gambles with his leadership ("I used to roll the dice"). He took over other kingdoms, replacing the old kings in the other kingdoms ("now the old king's dead long live the king")
One minute I held the key
Next the walls were closed on me
And I discover that my castle stands
Upon pillars of salt and pillars of sand
He once held power over many things and had the keys to many kingdoms, but time flew so quickly that he lost those riches. "Castle" here refers to his power, and it was said that it was upon pillars of salt, which I think refers to the Bible where Lot's wife turned to a pillar of salt when she looked back, and pillars of sand, like what the bible said "the stupid man built his house over sand". Pillars of salt and sand means that the foundation to his power are very weak.
I hear Jerusalem bells are ringing
Roman Calvary choirs are singing
Be my mirror, my sword, and shield
My missionaries in a foreign field
And for some reason I can't explain
Once you'd go there was never
Never an honest word
And that was when I rule the world
" I hear Jerusalem bells..etc" are all religious. "Be my mirror" means be my image, sword means power, shield means strength/protection. "Missionaries in a foreign field" means he was a religious person and went to other countries to preach. The king had become a tyrant, and he never told an honest word. "i know Saint Peter won't call my name" means that he had been a very bad person and it was said that Saint Peter will call your name if you are qualified to enter heaven, so he knew that his name won't be called.
For me this song is very interesting because the lyrics are masked, and I like how the percussions and strings used in the song made it very enjoyable.
It also taught us that our comfort won't last forever, and we can lose it anytime. In the lyrics, the writer described a king who had become a corrupt person, and now he have nothing. It made people reflect on their lives, whether they have make most of their lives or not. I recommend this song to everyone of every ages, especially to those who are succesfull and thought that they are the king of the world.