Deuteronomy 4:15

Take ye therefore good heed unto yourselves
As to keep all the laws given them, so particularly to avoid idolatry:

for ye saw no manner of similitude on the day the Lord spake unto you
in Horeb out of the midst of the fire;
and therefore, as they had nothing that directed and led them, so they had nothing that could be a temptation to them, to make any form or likeness, and worship it.