There is a difference in understanding, belief, and faith.
Understanding is getting facts and information lined up so that you "see" it in your mind. It is rational to you. It makes good sense.
Belief is agreeing with the facts or information set before you. It is agreeing with a scientific fact, or spiritual idea, or physical facts, or any other kind of facts. When you don't believe it, you don't accept the information given to you. Believing God and believing the Bible sounds good, but it is not nearly enough. You need to put your faith in God, his word, and his commands.
Faith is much more than believing. The demons believe in God and they shudder, it says in James 2:19. They believe, but they don't have faith. They believe more than most so-called Christians do today. They have seen God do much more than we have. But they don't have faith.
...