Yet more quotes from J.I. Packer’s “Knowing God”:
Psychologically, it is certain that if you habitually focus on your thoughts on an image or picture of the One to whom you are going to pray, you will come to think of Him, and pray to Him, as the image represents Him. Thus you will in this sense “bow down” and “worship” your image; and to the extent to which the image fails to tell the truth about God, to that extent you will fail to worship God in truth. That is why God forbids you and me to make use of images and pictures in our worship.
To make an image of God is to take one’s thoughts of Him from a human source, rather than from God Himself; and this is precisely what is wrong with image-making.