Should keep knowledge — It is this that their office binds them to; it is the duty of all God's people to know his law, but the priest's duty to know it more than others. And they — The people.
Related Commentaries of Malachi 2:7
Malachi 2:7
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.