"I have yet many things to say to you, but you cannot bear them now. However, when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatever he shall hear, that shall he speak: and he will show you things to come" (John 16:12-13).
The Bible records that the Lord Jesus said to Peter, "And I will give to you the keys of the kingdom of heaven: and whatever you shall bind on earth shall be bound in heaven: and whatever you shall loose on earth shall be loosed in heaven." (Matthew 16:19).
God’s assessment of Job is, “That there is none like him in the earth, a perfect and an upright man, one that fears God, and eschews evil” (Job 1:8).
What's the danger if we believe in God based on the viewpoint "seeing is believing"? The author found the reason of Thomas' failure through investigating, which enlightened him. He came to realize how to believe in God in order to obtain His praise.