2:7 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.

Malachi 2:7 Parallel Commentaries

Whether Knowledge of all Holy Writ is Required?
Objection 1: It would seem that knowledge of all Holy Writ is required. For one from whose lips we seek the law, should have knowledge of the law. Now the laity seek the law at the mouth of the priest (Malachi 2:7). Therefore he should have knowledge of the whole law. Objection 2: Further, "being always ready to satisfy everyone that asketh you a reason of that faith and hope in you [*Vulg.: 'Of that hope which is in you; St. Thomas apparently took his reading from Bede]." Now to give a reason for …
Saint Thomas Aquinas—Summa Theologica

A Dialogue with God
'The Lord will cut off the man that doeth this ... out of the tents of Jacob, ... 14. Yet ye say, Wherefore? Because the Lord hath been witness between thee and the wife of thy youth.'--MALACHI ii. 12, 14 (R.V.). It is obvious from the whole context that divorce and foreign inter-marriage were becoming increasingly prevalent in Malachi's time. The conditions in these respects were nearly similar to that prevailing in the times of Ezra and Nehemiah. It is these sins which the Prophet is here vehemently …
Alexander Maclaren—Expositions of Holy Scripture

Of Orders.
Of this sacrament the Church of Christ knows nothing; it was invented by the church of the Pope. It not only has no promise of grace, anywhere declared, but not a word is said about it in the whole of the New Testament. Now it is ridiculous to set up as a sacrament of God that which can nowhere be proved to have been instituted by God. Not that I consider that a rite practised for so many ages is to be condemned; but I would not have human inventions established in sacred things, nor should it be …
Martin Luther—First Principles of the Reformation