Malachi’s generation questioned God’s presence and justice (2:17). For the rest of the book His justice and knowledge of their ways is stated. Warning those who don’t fear Him of grave judgment, but glory for His remnant.
Here we have priest who don’t believe what they represent. They were dressed up as believers and that is all. Bluntly God warns them to obey or be cursed. With graphic and severe language they are promised judgment.
Using a question and answer format God indicts a derelict people who are determine to deny His charges. Their sinful ways were the products of not taking Him seriously. Indictments from men require proof, from God they come proven.