The Emperor is a figure of severity, someone upholding order that must be obeyed. In simple terms the Emperor represents a father figure, a masculine force who lays down strict rules and demands obedience. After all, we need firm boundaries so that we can work within a system where we aren't fighting every moment of our lives to survive.
Rules and laws are necessary in society to stop chaos, and institutionalised power provides necessary order to maintain a peaceful society. In this context the Emperor symbolises the rules and laws of government, both good and bad, and the power to enforce them. The stability derived from such order provides safety and security so that we contemplate our higher spiritual purpose.
The Emperor provides measurement over emotion, so that we can rely on predictable order for the greater good of ourselves and the society we live in.
In a reading: Order, Rules, Laws, Control, Ambition, Power, Control, Rational thinking, Father, Firm boundaries, Stability, Coldness, Hardness, Aggression, Dominating figure, Inflexible, Government systems = An assertive card, this is a card that says yes, there is nothing indecisive about it, it's full steam forward in the belief that it must dominate and control to uphold the law.