What does the cover on Flyleaf's CD Memento Mori mean?

'Memento Mori' meaning "Remember you're mortal". And whenever the king would came back from a war or something, there would be a parade. But a slave would be behind him saying "Memento Mori", meaning, "You're just like the rest of us. Remember, you will die one day. You don't exceed that rule". So the king is on the front, and there arer Trumpet players for the "parade" and them Lacey is the slave saing 'Memento Mori!'.

-Hoped this helped.