Seeing the invisible consists in polishing its ability to identify a metaphysical, susceptible content capable of surpassing the outward appearance of phenomena and surrendering their inner essence to those who can observe.
It is indeed an abstract consideration, but it can be easily understood if applied to the arts. When you look at a painting, you see the painting, but behind that painting is the expression of an artist. You can identify feelings such as anguish, happiness, sadness, etc.