The mirror is there to help us evaluate what we look like. And James is asking, what is the use of the mirror if you do not do anything about [what you see]. What is the use of the mirror if you do not do anything about the egg you have spilled on your jersey, or the [messy] hair, or the immodesty of your clothing? Then it is of no use! Then the mirror did not play any role. That is what James is saying. It did not help. The mirror is there to help us sort things out so that we can change things. And James says, that is the way the Word works. The Word is a mirror to our lives; it exposes our sin. It shows us where we need to repent and live a different way. To have soft hearts that are repentant every day as our sin is exposed every day.1
Thomas Schreiner
23 For if anyone is a hearer of the word and not a doer, he is like a man who looks intently at his natural face in a mirror.