Neither let us commit fornication ... - The case referred to here was that of the licentious contact with the daughters of Moab, referred to in Numbers 25:1-9.
And fell in one day - Were slain for their sin by the plague that prevailed.
Three and twenty thousand - The Hebrew text in Numbers 25:9, is twenty-four thousand. In order to reconcile these statements, it may be observed that perhaps 23,000 fell directly by the plague, and 1,000 were slain by Phinehas and his companions (Grotius); or it may be that the number was between 23,000 and 24,000, and it might be expressed in round numbers by either - Macknight. At all events, Paul has not exceeded the truth. There were at least 23,000 that fell, though there might have been more. The probable supposition is, that the 23,000 fell immediately by the hand of God in the plague, and the other thousand by the judges; and as Paul’s design was particularly to mention the proofs of the immediate divine displeasure, he refers only to those who fell by that, in illustration of his subject - There was a particular reason for this caution in respect to licentiousness:
(1) It was common among all idolaters; and Paul in cautioning them against idolatry, would naturally warn them of this danger.
(2) It was common at Corinth. It was the prevalent vice there. To “Corinthianize” was a term synonymous among the ancients with licentiousness.
(3) So common was this at Corinth, that, as we have seen (see the introduction), not less than 1,000 prostitutes were supported in a single temple there; and the city was visited by vast multitudes of foreigners, among other reasons on account of its facilities for this sin. Christians, therefore, were in a special manner exposed to it; and hence, the anxiety of the apostle to warn them against it.