Nehemiah 10:30

And that we would not give our daughters unto the people of the land, nor take their daughters for our sons:

The verse belongs to the gathering of the people in Jerusalem after the wall had been rebuilt, when Ezra blessed God and the people worshiped. It is part of a solemn covenant made by the whole congregation after praise and a recounting of Israel's history of great divine goodness met with great ingratitude, after the people had suffered punishment for sin and acknowledged the justice of God's dealings. In that covenant the people pledged to walk in God's law given through Moses and to observe and do all His commandments, judgments, and statutes. The verse records one specific promise within that oath, that they would not give their daughters in marriage to the peoples of the land nor take those peoples' daughters for their sons.

To make it a sure covenant preserved in permanent form as a memorial of obligation, it was written out and signed by priests, Levites, and princes, to serve as a reminder of duty and a barrier against temptation. Intermarriage with other nations was evidence of sin and had contributed to the corruption of the Hebrew language.