ודברתם אל הסלע לעיניהם… (חקת כ:ח)

Why does it say “to their eyes” when one can only hear with their ears?  Hashem wanted the Yidden to reach a lofty level when they received the Ten Commandments.  We read in the Torah “וכל העם רואים את הקולות,” and the entire nation saw the sounds – yes, they could see with their eyes what one can only hear with one’s ears.  Such a level can be obtained only when holy words are spoken, affecting the eyes as much as the ears.