Nehemiah 13:23

In those days also saw I Jews that had married wives of Ashdod, of Ammon, and of Moab:

This took place after the Jews had publicly pledged themselves to obey God's law, during Nehemiah's absence in Persia when his restraining influence was withdrawn and evils crept in that threatened to pervert the nation. In those days Jewish men married wives and women from Ashdod, from Ammon, and from Moab. Those marriages were unhallowed intermarriage and unlawful alliance and association with idolaters that brought great confusion into Israel and threatened to pervert the nation and bring it to ruin if the evil continued.

They were in direct defiance of God's word through Moses that Ammonites and Moabites should be forever shut out from the congregation of His people because of their cruelty and treachery toward Israel. They violated God's commands and threatenings not to give their daughters to idolaters' sons nor to take idolaters' daughters for their sons. Tobiah the Ammonite was Israel's bitter enemy, a representative of a proscribed race and an enemy of God and His truth, and the friendship and alliance made with him by intermarriage, even by Eliashib the high priest, showed contempt for God.

The evil was made worse because some who entered into these marriages were men in high position and rulers to whom the people had a right to look for counsel and safe example. The children of these marriages spoke half in the speech of Ashdod and the languages of those peoples rather than the Jews' language and could not speak the Jews' language. Intermarriage and family life with idolaters brought heathen customs into Israel, and children raised in those customs became idolaters, a serious danger because they remained connected to God's people. It was the same great evil by which idolatrous women turned even King Solomon, to whom God had given wisdom like no other king among the nations, away from God and corrupted Israel. It was a sin for which fearful judgments had come on Israel in the past, and which required earnest reasoning, stern rebuke, aroused conscience, and reformation to turn away God's threatened anger and bring His approval and blessing.