http://biblia.com/books/nrsv/Ne13.1
Ezra-Nehemiah's prohibition on intermarriage reflected a deep concern for establishing and regulating community boundaries (cf. Neh. 13:23-27).
The "law" in Ezra-Nehemiah was intended to fashion (note constructivist and not descriptive) the social-political order into one consistent with golah collective desire for land and authority.
Modern Relevance of Neh. 13?
Can Neh. 13 be used to support a position such as that advocated in the following?
Three pillars of monotheism:
Concepts of an exclusive God did not produce a monotheistic religion. The desire for exclusive authority and control over the land produced the idea of an exclusive God.