An Ammonite or Moabite - These nations were subjected for their impiety and wickedness, (see Deuteronomy 23:4 and Deuteronomy 23:5), to peculiar disgrace, and on this account were not permitted to hold any office among the Israelites. But this did not disqualify them from being proselytes: Ruth, who was a Moabitess, was married to Boaz, and she became one of the progenitors of our Lord.

Even to their tenth generation - That is, for ever, as the next clause explains; see Nehemiah 13:1.

enter into

Deuteronomy 23:1 He that is wounded in the stones, or has his privy member cut off, shall not enter into the congregation of the LORD.

Romans 3:29,30 Is he the God of the Jews only? is he not also of the Gentiles? Yes, of the Gentiles also...

Ephesians 2:12,13 That at that time you were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise...

third generation

Deuteronomy 23:2,3 A bastard shall not enter into the congregation of the LORD...

Exodus 20:5,6 You shall not bow down yourself to them, nor serve them: for I the LORD your God am a jealous God...

Reformation
[This chapter is based on Nehemiah 13.] Solemnly and publicly the people of Judah had pledged themselves to obey the law of God. But when the influence of Ezra and Nehemiah was for a time withdrawn, there were many who departed from the Lord. Nehemiah had returned to Persia. During his absence from Jerusalem, evils crept in that threatened to pervert the nation. Idolaters not only gained a foothold in the city, but contaminated by their presence the very precincts of the temple. Through intermarriage, …
Ellen Gould White—The Story of Prophets and Kings

Brief Directions How to Read the Holy Scriptures once Every Year Over, with Ease, Profit, and Reverence.
But forasmuch, that as faith is the soul, so reading and meditating on the word of God, are the parent's of prayer, therefore, before thou prayest in the morning, first read a chapter in the word of God; then meditate awhile with thyself, how many excellent things thou canst remember out of it. As--First, what good counsels or exhortations to good works and to holy life. Secondly, what threatenings of judgments against such and such a sin; and what fearful examples of God's punishment or vengeance …
Lewis Bayly—The Practice of Piety

Commerce
The remarkable change which we have noticed in the views of Jewish authorities, from contempt to almost affectation of manual labour, could certainly not have been arbitrary. But as we fail to discover here any religious motive, we can only account for it on the score of altered political and social circumstances. So long as the people were, at least nominally, independent, and in possession of their own land, constant engagement in a trade would probably mark an inferior social stage, and imply …
Alfred Edersheim—Sketches of Jewish Social Life