Sefer HaBahir 47

1[Mar Rachumai continued,] "And what is, 'And an image you did not see, only a voice' (Deuteronomy 4:12)? This is as Moses said to Israel, 'For you did not see all the image' (Deuteronomy 4:15) — [you saw] an image but not the whole image. A parable, to what it is may be compared: To a king that stands above his servants, draped in a white robe. It's not enough for the awe of the kingdom that they look at his garments. Further, the king was too far away, but they heard his voice. Can they see his throat? You would say, 'No.' Thus, you learned that they saw an image but not the whole image. Thus, it is written, 'And an image you did not see, only a voice' and it is written, 'The voice [i.e., sound] of words you heard' (Deuteronomy 4:12)."