What does James 1:23 mean?

This verse introduces a useful analogy, but it needs to be read in context with the prior two verses in order to have maximum impact. James compares looking into a mirror with looking into the law of God. The big idea will be that, in both cases, merely "looking" is not enough. We must retain what we see. We must act on what we see.

James begins the comparison in this verse by saying that someone who listens to the Word—the message of Jesus—but does not do what it says is like someone who looks at his own face in a mirror and, per the next verse, immediately forgets what he looks like.

It's important to be careful about what James is not saying here. We have to be careful not to read so much into the details of an analogy that we miss the actual point. James isn't saying that looking at the Word is exactly like looking at ourselves. He's bringing out an absurd example to make his point: To forget what God Himself has revealed to us through His Word, when we go out into the world to live, is as absurd as forgetting what we look like as soon as we walk away from a mirror.