Romans chapter 4 also teaches this truth. Faith is the very power that God Himself used to create the universe. It is the original, basic spiritual law around which everything happens in God's plan for the ages. Faith is not just mental assent or hope, but an absolute trust in the truth of something even in the apparent absence of any physical proof. By faith, even that which has no physical evidence becomes fact.
Some people pray for faith or pray for their faith to grow or be increased.
The father of the little girl didn't understand what Jesus told him, for just before asking Jesus to help his unbelief, Jesus said to him that anything is possible to him, if he only believed. Many state faith must be qualified according to God's will. This passage of scripture was written to carnal people, as the rest of James chapter 4 clearly shows. Their carnality is what makes them unable to know God's will. This doesn't apply to the Christian who is living according to God's Word.