Majesty describes a quality that takes your breath away, it's so impressive. The Grand Canyon has it, and so does a British monarch (supposedly).
The word majesty brings to mind a luxurious castle, which is appropriate because it is also used to address or refer to a king or queen. The Latin root word is maiestatem, which means "greatness, dignity, or excellence," and people first used the noun majesty to talk about God. It was England's King Henry VIII who decided that majesty would be the official way to address a British monarch.