Howbeit then, when ye knew not God, ye did service unto them which by nature are no gods.
Note 1 at Ga 4:8: Formerly, before the Galatian Christians came to know God through Christ, they were slaves to sin and in bondage to idols (1Co 12:2). These idols were gods in name only. They had no life and couldn't do anything good or bad (Ps 115:4-8, 135:15-18; Isa 44:9-20; and Jer 10:3-16). That's what Paul meant when he said, "Which by nature are no gods."