The old man's wisdom was a guiding light.
Meaning: It means that someone's wisdom was very helpful and insightful, like a light that guides you in the dark.
Choice of Words: Wisdom is the ability to make good decisions and judgments, and guiding light is something that helps you find your way. So, "The old man's wisdom was a guiding light" means that the old man's wise advice helped others make good decisions and find their way in life.
Alternative Expressions
Related Expressions