Romans 1:23

‘And changed the glory of the incorruptible God for the likeness of an image of corruptible man, and of birds, and four-footed beasts, and creeping things.'

So by setting up his idols man changed the invisible glory of the God Who could not suffer corruption, something revealed for example through His invisibility in the Tabernacle, and replaced it with the likeness of images in human and beastly form. Note the emphasis on the downward path. ‘The glory of the incorruptible God' was changed into ‘an image' which represented corruptible things. Then in many cases, in order to make these images impressive they had to make them huge. But it was all deceit. Priests even had secret ways into the Temples so that they could remove the food offerings and pretend that the gods had eaten them. They did not see themselves as deceptive, but as trying to inculcate faith. However, now at least they had gods whom they could control and who were not concerned about their moral behaviour.

It is very possible that here Paul had Genesis 1 in mind. There God, having created birds, beasts and creeping things, created man in the image and likeness of God, exalting him above all creation, in order that man might look off to Him. Here man has reversed the situation. He has created gods in the image and likeness of himself, and of the birds, four-footed beasts and creeping things which God had created, debasing everything including himself, so that he might not have to look off to God. Paul's thought is probably also loosely based on Psalms 106:20, where, speaking of the incident of the molten calf in the wilderness, it says, ‘they changed their glory into the likeness of an ox which eats grass.' They had replaced the glory of God for something that sustained itself on grass. This was typical of the actions of fallen man.

‘The glory of the incorruptible God.' There were many times when God's glory descended on the Tabernacle, leaving a firm impression of His glory, majesty and holiness, and of His ‘otherness', something which was then recorded so that others might appreciate it too. At other times the people were awed at the thought of His invisibility, or at the thought that He was alone in majesty behind the curtain in the Holy Place, among them and yet remote and unique. But all knew that He did not wear out or grow old. It was very different with the images that they introduced into the Temple in the days of disobedience. They had to be replaced and disposed of. It was in the days of disobedience that the idea of the glory of God, and of His incorruptibility, were lost in nominal Yahwism, with all the focus being on the grotesque idols.