Vague realities... take the past, present, and future. Can we define the boundary points between each? If we could, we may find the present is the very instant at which the future becomes the past, in which case the present is gone before you know it! If something so widely accepted as the past, present, and future is actually so undefinable, what other vague realities are we accepting?
Sickness? Germs, viruses, etc. are all over the place. At what point do they constitute sickness? Depends upon the individual's immune system? How is the immune system measured? hmmm...
Sin? Only the self-righteous bigot has this one nailed down. Our textbook opens with Shakespeare's insight: "There is neither good nor bad, but thinking makes it so." And how do we definitively measure good or bad thinking? hmmm...
Death? How many times have people been declared dead by the usual standards and then are discovered to be quite alive after all? The out-of-body experiences, consciousness continuing after the brain stops, etc., remain inexplicable to physics. hmmm...
In this light, the outrageous assertion in our textbook is not so outrageous: "Sickness, sin, and death are the vague realities of human conclusions." And turning to something beyond human conclusions for reality should be the natural outcome of thoughtful consideration.
"What is termed material sense can report only a mortal temporary sense of things, whereas spiritual sense can bear witness only to Truth...
Spiritual sense, contradicting the material senses, involves intuition, hope, faith, understanding, fruition, reality. Material sense expresses the belief that mind is in matter. This human belief, alternating between a sense of pleasure and pain, hope and fear, life and death, never reaches beyond the boundary of the mortal or the unreal. When the real is attained, which is announced by Science, joy is no longer a trembler, nor is hope a cheat. Spiritual ideas, like numbers and notes, start from Principle, and admit no materialistic beliefs. Spiritual ideas lead up to their divine origin, God, and to the spiritual sense of being." (S&H)
Listen to larger context here.