1 Corinthians 6:16

What? know ye not that he which is joined to an harlot,
&c.] Not in marriage, but in carnal copulation, and unclean embraces, is one body with her

for two
("saith he", Adam, or Moses, or God, or the Scripture, or as R. Sol. Jarchi says, the Holy Spirit, ( Genesis 2:24 ) )

shall be one flesh;
what is originally said of copulation in lawful marriage, in which man and wife, legally coupled together, become one flesh, is applied to the unlawful copulation of a man with an harlot, by which act they also become one body, one flesh; and which is made use of by the apostle, to deter the members of Christ from the commission of this sin, which makes a member of Christ one body and flesh with an harlot, than which nothing is more monstrous and detestable. The apostle here directs to the true sense of the phrase in Genesis, "and they shall be one flesh"; that is, man and wife shall only have carnal knowledge of, and copulation with each other. Some Jewish ^F11 writers interpret this phrase, (dlwh dum) "on account of the foetus", which is formed by the means of them both, and which becomes "their one flesh": others ^F12, thus as if they were, or because they are, like as if they were one flesh; but others ^F13, in more agreement with the apostle, think that this has respect (rwbxh la) , "to that conjunction", by which the fixing of the species is completed; and others ^F14 expressly thus, "they two shall be one flesh", (dxa rvb Myvwe Mhynvv Mwqml) , "that is, in the place where both of them make one flesh": which is equally done by unlawful copulation with an harlot, as with a man's own wife.