348. (13) Polygamy is not a sin among people for whom it is in accordance with their religion. Everything that is contrary to a person's religion is believed to be a sin because it is contrary to God; and conversely, everything that accords with religion is believed to be not a sin because it accords with God. So, because polygamy among the children of Israel was in accordance with their religion, and similarly today among Muslims, it could not and cannot be imputed to them as sin. Moreover, to keep it from being a sin with them, they remain natural and do not become spiritual. And the natural man cannot see anything sinful in such things as are matters of the accepted religion. That is something only the spiritual man sees. It is for this reason that although Muslims in accordance with the Koran acknowledge our Lord as the Son of God, still they do not go to Him but to Muhammad. And as long as they do that, they remain natural, and consequently do not know that there is anything evil, not even anything lecherous, in polygamy. The Lord even says:
If you were blind, you would have no sin. But now you say that (you) see; therefore your sin remains. (John 9:41)
Since polygamy cannot indict them of sin, therefore they have their own heavens after death (nos. 342, 343); and they experience joys there in accordance with their life.