Everyone believes in something: the difference in the “who” or the “what” in which we place our absolute trust.
The atheist believes in himself.
The moralist believes in the virtue of his personal merit, goodness or ideals.
The religionist believes in rituals and rites.
The Hindu believes in millions of gods.
The legalist believes in the power of rules and obedience to those rules.
Each of these exercises faith, but only the Christian trusts in Jesus Christ without any faith in self.
The world is full of those who say they believe in God; but believing something in the head is not enough. James 2:19 says that even the demons believe that God exists and tremble at the thought; however, they do not trust in Jesus alone to make them right with God the Father.
We are the circumcision, who worship God in the Spirit, rejoice in Christ Jesus, and have no confidence in the flesh (Philippians 3:3). You are sons of God through faith in Christ Jesus (Galatians 3:26).