All of the words in the Torah translated as 'obey' are variations on 'shema', 'listen'. God explicitly forbids making any sort of image to be used in worship - even worship of Him. Seeing and listening provide two very different levels of understanding. Seeing is superficial and detached from the one being observed. It tells nothing of what's going on inside. Listening, on the other hand, can provide an entirely different level of understanding, since it goes past the superficial and and allows the speaker to expose what's inside.