This is a fantastic explanation of Exodus 20.4 by Jewish scholar Nahum Sarna.
“The revolutionary Israelite concept of God entails his being wholly separate from the world of his creation and wholly other than what the human mind can conceive or the human imagination depict. Therefore, any material representation of divinity is prohibited, a proscription elaborated in Deuteronomy 4:12, 15-19, where it is explained that the people heard ‘the sound of words’ at Sinai ‘but perceived no shape – nothing but a voice.’ In the Israelite view any symbolic representation of God must necessarily be both inadequate and a distortion, for an image becomes identified with what it represents and is soon looked upon as the place and presence of the Deity. In the end the image itself will become the locus of reverence and an object of worship, all of which constitutes the complete nullification of the singular essence of Israelite monotheism.”
Found on page 110 of Exodus in the JPS Torah Commentary series.