HEARING AND DOING
James gives us a clear instruction, which, put very simply, means: "If you spot any sin in your life, get rid of it!"
Having given us this instruction, James tells us to be "doers of the word, and not hearers only." James then seems to illustrate this with a word picture of two mirrors.
When we look into a NATURAL mirror, one made of glass, we see ourselves as we are. We see what we expect to see. As James says, the man who looks at himself in such a mirror sees himself and then goes away, forgetting what he has seen. BUT, when a man looks into a SPIRITUAL mirror, he sees the sort of man God wants him to be. He looks into the "perfect law of liberty", God's Word, and IF HE OBEYS, he will become the sort of man God wants him to be.
The greatest thing a Christian can do is simply obey God. Obedience makes all the difference. If we say we are Christians, but don't obey God, we are like the man who looks in the spiritul mirror, but doesn't try to become the sort of person God wants him (or her) to be.
All through the Bible, obedience is linked to faith. If we really believe that what God says is true, we will obey. This is why we are told to "believe" in Jesus. The Greek word for "believe" means "to be subject to" or to "submit to".
A "doer of the word" has already bowed their knee to the Lord Jesus. Anyone who says they are a Christian, but doesn't obey Him is suspect - they may not even be a Christian. This is one way of telling the difference between true Christians and fakes.