Translation
You know that when you were nations, you were being led away
Go to footnote numberto the soundless idols, in the manner in which you were led. (See comment below.)
Paraphrase
You know that when you were Gentiles, you were seduced and led astray, in whatever manner you were led, to speechless idols which cannot teach you truth. (See comment below.)
Footnotes
1
“led away” comes from two words – from the preposition “away” and the verb “to carry, take, lead.” Putting those two words together brings the meaning of “seduce, lead astray.”
Don't Be Seduced and Led Astray Again
It does not matter what method was used to seduce them and lead them astray the first time, it only matters that it happened. Paul does not want it to happen again. He may be saying this because some among those of the Corinthian church are in danger of being seduced, or have already been seduced, regarding the topic Paul has just entered.