James 2:14 – Dear brothers and sisters, what’s the use if saying you have faith if you don’t prove it by your actions?  That kind of faith can’t save anyone. (NLT)
It is not enough to believe you will win a fight or competition.  You have to put in the time, training, and preparations.  You have to act on that belief you will win.  If you do not, you will lose.  Fighters who do not take action to get ready will become flat footed, slow, and will clam up when the pressure hits.
In our Christian walk, the same is also true.  Believing should produce action.  If we truly believe in the Gospel of Christ, we cannot just believe people are being saved, even though they are.  It should move us so much, we act on the good news of Jesus Christ so others may know.  God gives us opportunities everyday to introduce people to Christ.
Our lives should also show our faith in Christ by the fruit it produces.  If we do not, we look pretty much like the world.  We do not lead by example, and can taint the image of God.