We need to feed upon God's word and remember what God has said. John needed to hold to his former belief and conviction about Jesus Christ. He may be baffled and puzzled by the turn of events that led him to prison, but he could continue to trust God. Even Martin Luther in one of his moods of depression felt as if Satan himself was closing in upon him. There is a type of unbelief that causes us to question what we believe as we search for deeper understanding .
Honest doubt can be the steppingstone to a strong faith.
History, for instance, is literally patched together by doubt. There could be no progress without it. Galileo doubted that the earth stood still. Copernicus doubted that the earth was the center of the universe. Columbus doubted that it was flat.