“‘Cursed be anyone who lies with his mother-in-law.’ And all the people shall say, ‘Amen.’
When the law was written, to be seen and read by all men, the sanctions of it were to be published, which, to complete the solemnity of their covenanting with God, they were deliberately to declare their approbation of. This they were before directed to do (Deu 11:29, Deu 11:30), and therefore the appointment here begins somewhat abruptly, Deu 27:12.
Commenting on Deuteronomy 27:11-26
Cursed be he that lieth with his mother in law,.... See Lev 18:7. All these incestuous or brutal copulations may well be supposed to be done in secret: and all the people shall say Amen; as abhorring such incest.
Cursed [be] he that lieth with his mother in law. And all the people shall say, Amen. (n) Meaning, his wife's mother.