How is the Word of God like a mirror?

For if anyone is a hearer of the word and not a doer, he is like a man observing his natural face in a mirror; for he observes himself, goes away, and immediately forgets what kind of man he was. But he who looks into the perfect law of liberty and continues in it, and is not a forgetful hearer but a doer of the work, this one will be blessed in what he does. James 1:23-25