Adam Clarke on Ruth 4:13

So Boaz took Ruth - The law of Moses had prohibited the Moabites, even to the tenth generation, from entering into the congregation of the Lord; but this law, the Jews think, did not extend to women; and even if it had, Ruth's might be considered an exempt case, as she had been already incorporated into the family by marriage; and left her own country, people, and gods, to become a proselyte to the true God in the land of Israel.