Charles Ellicott Commentary Leviticus 20:14

"And if a man take a wife and her mother, it is wickedness: they shall be burnt with fire, both he and they; that there be no wickedness among you." — Leviticus 20:14 (ASV)

A wife and her mother. —See Leviticus 18:17.

They shall be burnt with fire. —This, as we have seen, is the second of the four modes of capital punishment . In the following ten cases, those guilty of the sins specified suffered this punishment:

1. The unchaste high priest’s daughter (Leviticus 21:9);
2. He who had intercourse with his daughter;
3. Or with his daughter’s daughter;
4. Or with his son’s daughter;
5. Or with his wife’s daughter;
6. Or with her daughter’s daughter;
7. Or with her son’s daughter;
8. Or with his mother-in-law;
9. Or with the mother of his mother-in-law; and
10. Or with the mother of his father-in-law.

It will thus be seen that, with the exception of the high priest’s daughter, this death was only inflicted for incest.

As the Bible nowhere states the precise mode in which this kind of death was to be carried out, the authorities during the Second Temple maintained that it must be executed in such a manner as to leave the body externally unchanged by the flames. This was because, when God himself inflicted this punishment, the dead bodies of Nadab and Abihu were in a perfect state of preservation .

To effect this, the criminal was put into dung up to his knees. A soft cloth containing a hard one was then tied around his throat. The two witnesses who had secured his sentence then drew the two cords tighter until the criminal opened his mouth. Molten lead was then poured down his throat, thus burning him to death.

Hence, the ancient Chaldee Version renders it here: “They shall be burnt with fire, with melted lead in their mouth.”