Two Reasons Why Porneia Cannot Be Referring to a Marriage between Believer and Unbeliever

The word porneia in Second Temple Judaism can include marriages between believer and unbeliever. Since marriage is for the purpose of bringing up godly offspring, an unequally yoked marriage can be viewed as anticreational in that it threatens the covenant faithfulness of the children involved.

Hence, some might conclude that Jesus is talking about unions between believers and unbelievers when he uses the term porneia. Here are two reasons why I don't think this is the case.

1. If Jesus was referring to the union of a believer and unbeliever as porneia, then he would have been addressing he issue of an unequally yoked marriage. Yet, Paul, in 1 Cor 7:15 indicates that Jesus did not address this issue. If we understand that his switching between what the Lord commanded and what he commands as that which the Lord addressed in his earthly ministry versus what Paul is addressing now in the Spirit, then Paul would be arguing that the Lord did not address this union. Hence, porneia does not refer to this.

2. If the union between an unbeliever and believer is porneia, then Paul would be commanding, contrary to the Lord, that the two should remain together when it is up to the believer, and thus, that the believer should remain in a sexually immoral relationship/porneia. Yet, Paul argues that one should get married for the purpose of avoiding porneia, so why would he tell a believer to remain in porneia, especially if the Lord said it was legitimate to divorce for that reason.

Furthermore, the anticreational nature of it is addressed in that a believer who seeks to remain married to an unbeliever seeks to make his children "holy," and keeps the one flesh union intact. Hence, even this relationship can be creational and may be anticreational to seek a divorce from it, since the children are threatened as no longer being holy if the believer should be out of the household.

For these two reasons, I don't think it is legitimate to conclude that porneia in Matthew 5 and 19 includes marriages to unbelievers.