Man's domain is the earth. God gave him five senses to help him learn about his surroundings and to help him survive. Those senses are sight, hearing, taste, touch and smell. Though they are most useful to earthly life, they cannot sense spiritual realities. That is left to the human spirit. To try and judge what is spiritual by previous, or current, sensory information, leaves a person with little or nothing to go on. If man relies only on his senses, his understanding and knowledge will be very limited, or "narrow." The scope of what has been created by God is far greater, encompassing both the "visible and invisible" and "all things" (Colossians 1:16). Most of what we believe, as humans, is based on our past experience(some of which is based on imperfect, subjective perception). If we make our judgments and decisions based only on our experience, and the resulting understanding and knowledge ,we can find ourselves in such a narrow place that the life God intended for us is squeezed out. Think about it.