Igros Moshe on Lot's Daughters
BH a piece from the Igros Moshe regarding Lot's daughters was
embeded into Parshas Vayeira
https://zissel.org/subject/parshat-vayeira
The daughters of Lot were from the family of Avrahom and were miraculously saved from Sodom, therefore they could have claimed that they had not become pregnant from an immoral relation, rather another miracle had occurred for them and they become pregnant from the Shechina. Some people would have believed them and a new religion like Christianity could have emerged. To prevent this, they named their sons; Ammon and Moav, to declare that any time a woman becomes pregnant, there was always a human father. In merit of this intent, they merited that the True Moshiach will descend from them[75] via Rut the Moavite and Naama the Ammonite.
[75] Hakdama Igros Moshe
The daughters of Lot were from the family of Avrahom and were miraculously saved from Sodom, therefore they could have claimed that they had not become pregnant from an immoral relation, rather another miracle had occurred for them and they become pregnant from the Shechina. Some people would have believed them and a new religion like Christianity could have emerged. To prevent this, they named their sons; Ammon and Moav, to declare that any time a woman becomes pregnant, there was always a human father. In merit of this intent, they merited that the True Moshiach will descend from them[75] via Rut the Moavite and Naama the Ammonite.
[75] Hakdama Igros Moshe