As an example of how it's done, consider the New York Times piece explaining
that, originally, the holiness code in Leviticus did not prohibit
homosexuality as it now does, but only homosexual incest: unions
between a man and his father, brother, uncle, etc. A later editor
changed the prohibition, but we can rest content because that's not the
"Now, apply this principle to Leviticus 18: A law declaring that homosexual incest is prohibited could reasonably be taken to indicate that non-incestuous homosexual intercourse is permitted. . .It seems that with the later introduction in Leviticus of a law banning all male homosexual intercourse, it became expedient to bring the earlier material up-to-date by doing away with two now-superfluous injunctions against homosexual incest — injunctions that made sense when sex between men was otherwise allowed."
(The Secret History of Leviticus, by Idan Dershowitz, July 21, 2018, New York
Thus we learn that, before there was a ban in place against homosexual conduct in general,
homosexual incest was forbidden. Why, one wonders? Homosexual
intercourse never, in nature, results in offspring. Reticence to
engage in incest seems to be inborn to an extent, but some
societies have managed to tame the gag-reflex: Egypt and Persian
permitted brother-sister unions. One can well imagine, even
operating from an Enlightenment assumption that no law ever came
down from on high, that observant Egyptians and Persians must
have noticed the likelihood of birth defects is higher in these
unions. Thus popular pressure against heterosexual incest is
understandable. Against homosexual incest, with no underlying
understanding that homosexuality is wrong, not so much.
Utilitarian moral thinking is denied to man Biblically because
man does not know the future; God, who does know the future, is not
so limited. But God's legislation in the matter plainly goes beyond
concern for the accumulation of genetic errors in small breeding
populations. A man is not to have sex with his daughter-in-law, a
prohibition the unlettered Arabian prophet, Mohammed ibn Abdallah,
ran afoul of. He does not share a genetic lineage with her and so
the risk of birth defects is not the sole concern. But one
must suspect it is a concern.
Besides, it is not hard to see the rationale behind the expansions if we
follow the Bible's own logic. One principle that throws our New York Times author for a loop is the
Bible idea of 'one flesh.' Taking the concept literally, when a man
has sexual intercourse with a prostitute, he has sex, not only with
her, but with her entire sexual history: male, female, and other. It is enough to make
the client run to Family Dollar and buy a bottle of bleach! According
to Paul, “Shall I then take the members of Christ and make them members of a harlot? Certainly not!
Or do you not know that he who is joined to a harlot is one body with her? For 'the two,' He says,
'shall become one flesh.'” (1 Corinthians 6:15-16). This
concept mystifies our New York Times author, as does so much else in
the Bible, but it comes from taking very literally and very seriously the
Bible theme of 'one flesh.'