Albert Barnes Commentary Malachi 2:1

"And now, O ye priests, this commandment is for you." — Malachi 2:1 (ASV)

And now this is My commandment to you—not a commandment that He gave them, but a commandment concerning them. As God said long ago, upon obedience, I will command My blessing to you, so now He would command what should reach them, but a curse.

“He returns from the people to the priests, as the source of the evil, whose carelessness about sacred things He had rebuked before. Let the priests of the new law hear this rebuke of God, and understand it as dictated to them by the Holy Spirit, from whom God rightly requires greater holiness, and so He will punish them more severely if they are careless or scandalous in their office.”

All Christians are, in some sense, a royal, holy priesthood (1 Peter 2:9), over and above the special “Christian priesthood”; just as the Jews, over and above the special priesthood of Aaron, were a kingdom of priests (Exodus 19:6). Therefore, what follows belongs, in their own measure, to them and their duties.