Adam Clarke

For it is a shame even to speak - This no doubt refers to the Eleusinian and Bacchanalian mysteries, which were performed in the night and darkness, and were known to be so impure and abominable, especially the latter, that the Roman senate banished them both from Rome and Italy. How the discovery of these depths of Satan was made, and the whole proceedings in that case, may be seen in Livy, Hist. lib. xxxix. cap. 8-19, where the reader will see the force of what the apostle says here: It is a shame even to speak of those things which are done of them in secret; the abominations being of the most stupendous kind, and of the deepest dye.