Many people like to claim that John the Baptist lost his head over divorce and remarriage. Why did John the Baptist loose his head?
God chose not to make it clear in Scripture why it was unlawful for Herod to have his brother's wife. All Scripture says is that the marriage was unlawful. Scripture does not say why it was unlawful.
One early church writer said it was because Herod's brother died but was not childless, so therefore according to the OT law it was unlawful for Herod to take her as his wife. If this is true it is not a case of divorce and remarriage though many people would like to read that into the account.
I don't see how or why John would have been telling a pagan that what he was doing was unlawful, but apparently he did or else Herod or others were asking and forcing the issue.
So what "law" was John using to declare what Herod
had done as unlawful? Probably wasn't the Roman law. Weren't the
Jews still under the OT law at this time? Makes sense that it
was the OT law that made it unlawful, and under that law divorce
and remarriage was lawful but taking your brothers wife when she
was not childless was unlawful. The early church writer confirms
this was the case. John Coblentz also discusses this topic and
writes: "We
might note that this relationship fell
under the forbidden marriages of the Old Testament (see Leviticus
18:16)."