Albert Barnes Commentary Psalms 106:20

"Thus they changed their glory For the likeness of an ox that eateth grass." — Psalms 106:20 (ASV)

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).