New Defender's Study Bible Notes
13:3 mixed multitude. The “mixed multitude” (see Exodus 12:38) consisted of descendants of mixed marriages between the children of Israel and those from other nations. Those in the original mixed multitude (from Egypt or Edom) were accepted in the family of Israel after the third generation (Deuteronomy 23:7,8). However, those from such marriages with Moabites and Ammonites (Tobiah was an Ammonite) had been precluded from acceptance until the tenth generation (note Nehemiah 2:19; Deuteronomy 23:3).
13:4 before this. “Before this” probably refers to the considerable length of time it must have taken to accomplish the annulment of all the mixed marriages after the renewed covenant. Nehemiah had to go back to Babylon after serving some twelve years in Jerusalem (Nehemiah 13:6) and, while he was away, many people had already broken the promises of their covenant.
13:4 Tobiah. Tobiah was an Ammonite (Nehemiah 2:10) and an inveterate enemy of the Israelites. It is amazing that Eliashib, the chief priest, would actually give Tobiah a residence in the temple chamber where the tithes and offerings of the people were supposed to be stored. Nehemiah cast Tobiah out as soon as he heard of it.