Jehovah separated the tribe of Levi to bear the Ark of the Covenant of Jehovah, to stand before Jehovah to minister to Him and bless in His name until this day. Therefore Levi has no portion nor inheritance with his brothers; Jehovah is his inheritance, as Jehovah your God promised him.)......The priests, the sons of Levi, shall draw near; for Jehovah your God has chosen them to minister to Him and to bless in the name of Jehovah, and by their word shall every dispute and every assault be settled. Deut 10:8-9; 21:5.
The priests, Levi's descendants, were breaking the covenant by their sin, at Malachi's time in Israel's return from captivity. So the Lord through the prophet spoke to them, exposing them to help them. Jesus, being Jehovah incarnate, TriuneGodMan, is the Establisher and Mediator of a new and better covenant.
But you have turned away from the way; you have caused many to stumble at the law; you have corrupted the covenant of Levi, says Jehovah of hosts. Therefore I also have made you despicable and base before all the people to the same extent that you have not kept My ways but have been respecters of persons in the law.
A mediator is not a mediator for one, but God is one......There is one God and one Mediator of God and men, the man Christ Jesus......Now He has obtained a more excellent ministry inasmuch as He is also the Mediator of a better covenant, which has been enacted upon better promises...He is the Mediator of a new covenant, so that, death having taken place for redemption of the transgressions under the first covenant, those who have been called might receive the promise of the eternal inheritance...Jesus said to them, Truly, truly, I say to you, Before Abraham came into being, I am.