Deuteronomy 23:3 states:
> No Ammonite or Moabite or any of his descendants may enter the assembly of the LORD, even down to the tenth generation.

If this is so, why was David, one-fourth Moabite, not only a member of the assembly of the Lord, but King of Israel? Why was his grandmother, Ruth, admitted to the assembly?

The basic answer is that the command was not violated with Ruth, because in the ANE (and even today in the Near East) nationality was determined by fatherhood, so that any of Ruth's children were automatically Israelites and therefore eligible to be members of the assembly of the Lord. This is the concept of patrilineal descent. In fact, this is indicated in the Hebrew, where the verse uses the male pronoun exclusively to refer to those whom the command applies to.

It has been objected that this explanation does not square with Nehemiah 8:2, where the "congregation" consisted of men and women. The word "assembly" in Nehemiah 8:2 is qahal, and it is used in a generic sense, not the specific "assembly of the Lord."

Another objection points to Nehemiah 13:25, where the mixed congregation is told: "Ye shall not give your daughters unto their (Moab) sons, nor take their daughters unto your sons." It was considered a "great evil" to marry "strange wives" (Nehemiah 13:27). The objection is that this denounced "great evil" is exactly what occurred when Ruth married Boaz, and that Nehemiah 13:1 reiterates the exclusion of Ammonites and Moabites.

However, we are dealing with an entirely different social situation in Nehemiah wherein the male Jews were marrying foreign wives and allowing their cultural mores to supersede Jewish mores, leading to a sort of zealous nationalism. Nehemiah was disgusted to find that many of the children of these marriages did not speak the native tongue of Judah. The "great evil" was not the marriages themselves, but the pagan influence these "strange wives" were having on their husbands, who were supposed to be the ones converting the women to Judaism. The actions of that day were a calculated response to counter the influx of paganism. Furthermore, Nehemiah 13:3 says that "When the people heard this law, they excluded from Israel all who were of foreign descent." The foreign wives were not excluded until verse 23, which fits with the idea that wives of foreign descent, and their children, absorbed the nationality of the father.

Finally, some claim Deuteronomy 23:3 is a false prophecy. It is not a prophecy, but a command. There is a difference between being a resident living in Israel and being involved in the specific covenant relationship (citizenship in the nation of Israel). Exodus 12:48 shows there were aliens that fit that description. This does not mean Ruth would have been excluded from a relationship with Yahweh. A modern analogy is church membership: one can attend a church regularly for many years without officially joining.