Adam Clarke Bible Commentary
Fell in one day three and twenty thousand - In Num 25:9, the number is 24,000; and, allowing this to be the genuine reading, (and none of the Hebrew MSS. exhibit any various reading in the place), Moses and the apostle may be thus reconciled: in Num 25:4, God commands Moses to take all the heads (the rulers) of the people, and hang them up before the Lord against the sun; these possibly amounted to 1000, and those who fell by the plague were 23,000, so that the whole amounted to 24,000. Instead of εικοσιτρεις χιλιαδες, 23,000, two MSS., with the later Syriac and the Armenian, have εικοσιτεσσαρες χιλιαδες, 24,000; but this authority is too slender to establish a various reading, which recedes so much from the received text. I think the discordance may be best accounted for by supposing, as above, that Phineas and his companions might have slain 1000 men, who were heads of the people, and chief in this idolatry; and that the plague sent from the Lord destroyed 23,000 more; so an equal number to the whole tribe of Levi perished in one day, who were just 23,000. See Num 26:62; and see Lightfoot.
Jamieson-Fausset-Brown Bible Commentary
fornication--literally, Fornication was generally, as in this case (Num. 25:1-18), associated at the idol feasts with spiritual fornication, that is, idolatry. This all applied to the Corinthians (Co1 5:1, Co1 5:9; Co1 6:9, Co1 6:15, Co1 6:18; Co1 8:10). Balaam tempted Israel to both sins with Midian (Rev 2:14). Compare Co1 8:7, Co1 8:9, "stumbling-block," "eat . . . thing offered unto . . . idol."
three and twenty thousand--in Num 25:9 "twenty and four thousand." If this were a real discrepancy, it would militate rather against inspiration of the subject matter and thought, than against verbal inspiration. The solution is: Moses in Numbers includes all who died "in the plague"; Paul, all who died "in one day"; one thousand more may have fallen the next day [KITTO, Biblical CyclopÃ&brvbrdia]. Or, the real number may have been between twenty-three thousand and twenty-four thousand, say twenty-three thousand five hundred, or twenty-three thousand six hundred; when writing generally where the exact figures were not needed, one writer might quite veraciously give one of the two round numbers near the exact one, and the other writer the other [BENGEL]. Whichever be the true way of reconciling the seeming discrepant statements, at least the ways given above prove they are not really irreconcilable.
John Gill Bible Commentary
Neither let us commit fornication,.... To which the Corinthians were much addicted: hence the apostle elsewhere, in this epistle, makes use of arguments, to dissuade from it, as he does here, they judging it to be no evil:
as some of them committed; i.e. fornication; as they did at Shittim, with the daughters of Moab, Num 25:1 which was a stratagem of Balaam's, and the advice he gave to Balak king of Moab, to draw them into that sin, which made way for their commission of idolatry, which they committed by eating the sacrifices of their gods, and bowing down unto them; particularly they joined themselves to Baal Peor, the same with Priapus, one part of whose religious rites lay in acts of uncleanness, and this brought the divine displeasure on them:
and fell in one day three and twenty thousand; in Num 25:9 the number said to be "twenty and four thousand": and so say all the three Targums on the place (w), and both the Talmuds (x) and others (y); on the other hand, all the Greek copies of this epistle, and the Oriental versions, agree in the number of twenty and three thousand; so that it does not appear to be any mistake of copies, in either Testament. To reconcile this matter, or at least to abate the difficulties of it, let the following things be observed; as that the apostle does not write as an historian, and so not with that exactness as Moses did; besides, he does not say that there fell "only" three and twenty thousand, and this beings lesser number than is contained in his, and so a certain truth; moreover, Moses and the apostle use different words in their account; Moses says there died so many, including the heads of the people that were hanged up against the sun, and all that perished by the sword; the apostle says, that there fell such a number, referring only to the latter, who only could be properly said to fall, and not those that were hanged up: now the heads of the people that suffered the first kind of death, might, as is very probable, be a thousand; and they that died in the other way, three and twenty thousand, which make the sums to agree, and both are expressed by Moses, under the general name of a plague or stroke; to all this, that the apostle uses a limiting clause, which Moses does not, and says that these three and twenty thousand fell in one day. So that it is very likely that the heads of the people, supposed to be a thousand, were hanged up in one day; and the three and twenty thousand that fell by the sword died the next, which the apostle only takes notice of. Hence the Jew (z) has no reason to charge the apostle with an error.
(w) Targum Onkelos, Jon. ben Uzziel & Jerusalem in Numb, xxv. 9. (x) T. Hieros Sota, fol. 21. 4. T. Bab. Sanhedrin, fol. 106. 1. (y) Midrash Kohelet, fol. 68. 4. Tzeror Hammor, fol. 127. 3. (z) R. Isaac Chizzuk Emuna, par. 2. c. 36. p. 468.