John Calvin Commentary Galatians 4:8

"Howbeit at that time, not knowing God, ye were in bondage to them that by nature are no gods:" — Galatians 4:8 (ASV)

But when you did not yet know God. This is not intended as an additional argument; and indeed he had already proved his point so fully that no doubt remained, and the rebuke which was now to be administered could not be evaded. His object is to make their fall appear more criminal by comparing it with past events.

It is no wonder, he says, that formerly you did service to them which by nature are no gods; for wherever ignorance of God exists, there must be dreadful blindness. You were then wandering in darkness, but how disgraceful it is that in the midst of light you should fall into such gross errors!

The main inference is that the Galatians were less excusable for corrupting the gospel than they had formerly been for idolatry. But here it should be observed that, until we have been enlightened in the true knowledge of one God, we always serve idols, whatever pretext we may cast over the false religion.

The lawful worship of God, therefore, must be preceded by just views of his character. By nature, that is, in reality, they are no gods. Every object of worship which men contrive is a creature of their own imagination. In the opinion of men idols may be gods, but in reality they are nothing.