A holy life will make the deepest impression.
Lighthouses blow no horns, they just shine.
Once, as an experiment, the great scientist Isaac Newton stared at the image of the sun reflected in a mirror. The brightness burned into his retina, and he suffered temporary blindness. Even after he hid for three days behind closed shutters, still the bright spot would not fade from his vision. If he had stared a few minutes longer, Newton might have permanently lost all vision. The chemical receptors that govern eyesight cannot withstand the full force of unfiltered sunlight.