There is a vast difference between doubting faith and dynamic faith. Sometimes the doubts come and we are rendered weak and incapable of strong work because of doubts. Doubts are usually symptoms of something underneath the surface. First, sin may bring doubts.
Sin breaks the chain of faith.
Sin weakens your life. Sin blinds the eyes. Sin destroys your ability to lay hold upon truth. Sin tries to put the blame on another. Whenever you allow sin to invade your life, then, my friend, you can be sure that you will soon begin to have doubts.