Ezra 2:21

The children of Beth-lehem, an hundred twenty and three.

The children of Bethlehem who returned to Jerusalem in response to Cyrus's decree numbered one hundred twenty-three.
The number stands as a census entry given without further explanation.
It belongs to the list in Ezra 1-2 of the Jews already returned to Jerusalem and to their land with Zerubbabel in the first year of Cyrus under his proclamation.

The whole company already returned numbered 42,360 persons in all, distinct from the many Jews who still remained in Babylon and were invited to return.
The list records nearly fifty thousand people taking up the offer to return, showing that the captivity had ended in the sense that they were free to return.
The account belongs to the historical setting of the temple's rebuilding, showing the temple was begun under the decree of Cyrus and not in B.C. 457.
B.C. 457 marks the going forth of the commandment to restore and to build Jerusalem.