"Try, moreover, to turn your heart from the love of things visible and bring yourself to things invisible. For they who follow their own evil passions stain their consciences and lose the grace of God." Thomas a Kempis, Imitation of Christ
All things are full of weariness; a man cannot utter it; the eye is not satisfied with seeing, nor the ear filled with hearing." Ecclesiastes 1:8
We try so hard to substitute the invisible with the visible, but the more we seek to satisfy our longings with those things close at hand, the less our senses desire that which will truly fill us to the full.