Malachi is the last book of the Old Testament and belongs to the period of Nehemiah. The prophets message is to the priests and the people, charging them with indifference, doubt, and immorality. Malachi tells of the coming day of the Lord and closes the book with a prophecy of John the Baptist.

Malachi 2

2:7 For the priest's lips should keep knowledge, and they should seek the law at his mouth: for he is the messenger of the LORD of hosts.