Macbeth Act 1 Scene 7 Soliloquy

What is the central idea of Macbeth's soliloquy?

What literary device supports the central idea? Use a direct quote in your example/explanation.

Examples include: characterization, conflict, denotation/connotation, metaphor, simile, irony, language use, point-of-view, setting, structure, symbolism, theme, tone, etc.

Example: The central idea __________________________________ is supported by ___________. 

The line ____________________________ develops the central idea because________________________________________________________________________________.