In Nehemiah 10:21, the Israelites commit to not give their daughters in marriage to the surrounding nations, nor take their daughters for their sons. This commitment reflects their desire to remain faithful to God's commands and avoid the influence of foreign gods and practices. By maintaining purity in their relationships and honoring the covenant with God, the Israelites seek to preserve their identity as God's chosen people. This verse underscores the importance of obedience and separation from worldly influences in order to uphold their commitment to the Lord.