The First Reading today comes from Nehemiah, a man who had been an official under the Persian Emperor of Artaxerxes in 450 B.C., a time when Jerusalem was a subject of Persia.
Israel today sees Iran, the modern day Persia, as her chief enemy; so it is surprising to learn that in 450 B.C., the time of today's First Reading, Persia was Israel's protector.
Nehemiah, the author of today's first reading, was an official in the court of Persia's Emperor Xerxes. That emperor, on hearing that Jerusalem had fallen into the hands of an unlawful element, sent Nehemiah and the priest Ezra to Jerusalem, instructing them to find a way for bringing Jerusalem back to civility.
The way they found to straighten out Jerusalem, was to have the citizens commit themselves to following the ancient Mosaic Law. In today's reading, Nehemiah described how he and Ezra assembled Jerusalem's population before the Water Gate, where Ezra read out the ancient Mosaic Law while Nehemiah saw to it that the people agreed on living by that Law.