Thus they changed their glory - Their true glory - the proper object of worship - God. Compare the notes at Romans 1:23. They "exchanged" that as an object of worship for the image of an ox.
Into the similitude of an ox that eateth grass - Into the likeness of an ox. That is, They worshipped God under that image. The circumstance of its "eating grass" is added to show the absurdity of the act. Instead of worshipping God - an independent Being, who does not need to be supported, but who himself sustains all things, and provides for all - they worshipped an animal that had need of constant sustenance, and would itself soon die if deprived of its proper nourishment. Compare the notes at Isaiah 40:18-20; notes at Isaiah 41:6-7.

Thus they changed their glory - That is, their God, who was their glory; and they worshipped an ox in his stead. See the use St Paul makes of this, Romans 1:23 (note); see also the note there. The incorruptible God was thus served by all the heathen world.

Thus they changed their (k) glory into the similitude of an ox that eateth grass.
(k) He shows that all idolaters renounce God to be their glory when instead of him, they worship any creature much more wood, stone, metal or calves.

Thus they changed their glory,.... God, who is glorious in all the perfections of his nature, and is glory itself, and was the glory of these people; it was their greatest honour that they had knowledge of him, nearness to him, the true worship of him among them, and that they were worshippers of him; and who, though he is unchangeable in himself, may be said to be changed when another is substituted and worshipped in his room, or worshipped besides him; which was what the Heathen did, and in which the Israelites exceeded them, Romans 1:23, the Targum is,
"they changed the glory of their Lord.''
Into the similitude of an ox that eateth grass; which was monstrous stupidity, to leave the worship of the true God, El Shaddai, God all sufficient, all powerful, that stands in need of nothing, but upholds and supports all creatures in being, and provides them with necessaries; and worship an ox, yea, the figure of one that eats grass, that lives on hay, and is supported by that which is so weak and withering; the Targum adds,
"and makes dung;''
or defiles itself with it, as the ox does while it is eating grass; Jarchi observes, there is nothing more abominable and filthy than an ox when it is eating grass, which then makes much dung, and defiles itself; this the Targumist adds, to make the worship of such a creature the more contemptible.

Their glory - God, who was indeed their glory. Into - Into the golden image of an ox or calf, which is so far from feeding his people, as the true God did the Israelites, that he must be fed by them.