Sefer HaChinuch ספר החינוך

That an Ammonite or a Moabite not enter the Congregation of the Lord: That we should not marry with the males of the Children of Ammon and Moav forever, and even after they convert, as it is stated (Deuteronomy 23:4), “An Ammonite or a Moabite may not come into the Congregation of the Lord forever.”

What is explained in the section (of the Torah where it is mentioned) “because of the matter that they did not greet you with bread and water [...] and that he hired against you, etc.” is from the roots of the commandment. And the verse [thus] informed us of the greatness of the virtue of acts of loving-kindness, and the [need to] distance oneself from villainy and stinginess. And therefore He commanded us to fix a hatred for them; as they were wicked and abominable to show the fullness of their evil and villainy — not to greet a large congregation of those tired from the road, passing their border, with [even] bread and water; and that Moav hired Bilaam against them to curse them. And even though the Egyptians subjugated us and caused us pain for a long time, we only distanced ourselves from them to the third generation. And through this we knew that it is better for a person to do several sins rather than one great villainy — since in his willingness to do the ugly villainy and not to be concerned about revealing his opinion and his [lack of] embarrassment in front of the many peoples, he shows through it the evil of his constitution and the fullness of his lowliness. And [he also shows] that there is no way to fix and adjust himself to fix his deeds, and [that] his perversion is strengthened until ‘it cannot be fixed.’ And it is not fitting to mix such a person into the holy and blessed nation.

From the laws of the commandment is that which they, may their memory be blessed, said (Yevamot 76b) that specifically the males of the Children of Ammon and Moav — them and their sons forever — are the ones forbidden to come into the congregation, but the females are permitted immediately when they convert. And they said in explanation of this that it is since it is the way of the man to greet, but not the females; which is to say that their hand was not in this villainy when [the men] did not greet Israel with bread and water — since it is not the way of a woman to go out. And God would not twist justice to punish the woman for the villainy of the man — God forbid, that God would [allow such] evil. And the rest of its details are elucidated in the eighth chapter of Yevamot and at the end of Kiddushin. (See Tur, Even HaEzer 4.)

And this prohibition was practiced before King Sancheriv of Assyria came up against Jerusalem and exiled Israel, and also jumbled all of the nations and mixed them with each other — as he ruled over the whole [known] world. But after Sancheriv jumbled the nations and the Children of Ammon and Moav were mixed with the other nations of the world, all are permissible immediately after they convert; as there is an assumption that anyone who separates and comes to convert is separating from the other nations who are a majority (more numerous) with relation to the Children of Ammon and Moav and with relation to the Egyptians and the Edomites, as we will write about them adjacently (Sefer HaChinukh 563,564), with God’s help. And therefore we do not investigate anyone who converts in our time at all — as to which nation he is; but rather he is immediately permitted [regardless of the] nation he is from.