The Emperor symbolises measure over emotion, he is a figure of severity, upholding order which must be obeyed. He represents a father figure, masculinity enforcing strict rules and demanding obedience. Boundaries help us to work within a system so we aren't fighting every moment to survive.
In this context rules and laws are necessary to stop chaos, and institutionalised power provides order to maintain a peaceful society. The Emperor symbolises the rules and laws of government, both good and bad, and the power to enforce them. Stability derived from this order provides a peaceful society allowing us to contemplate our higher purpose.
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.