And now, O priests, this commandment is for you.
If you will not listen, and if you will not take it to heart,
to give glory to my name, says the LORD of hosts,
I will even send a curse upon you,
and I will curse your blessings:
yes, I have cursed them already,
because you do not take it to heart.
 

Behold, I will corrupt your seed,
and spread dung upon your faces,
even the dung of your solemn feasts;
and one shall take you away with it.
 

And you shall know that I have sent this commandment to you,
that my covenant might be with Levi, says the LORD of hosts.
My covenant was with him of life and peace;
and I gave this promise to him because of the respect he had for me,
and was afraid before my name.
The law of TRUTH was in his mouth,
and iniquity was not found in his lips:
he walked with me in peace and fairness,
and did turn many away from iniquity.
For the priest's lips should keep knowledge,
and the people should seek the law at his mouth:
for he is the messenger of the LORD of hosts.
 

          If you go to The Book of Ezekiel and read Chapter 34, you’ll get a better sense of what God was feeling when he gave Malachi this message for the priests. Why does the owner of the sheep choose certain shepherds? Because He trusts them to take care of His precious flock. The Levites (the shepherds) were leading the sheep (God’s people) astray instead of insuring their safety and the well being of their souls.

But you are departed out of the way;
you have caused many to stumble at the law;
you have corrupted the covenant of Levi, says the LORD of hosts.
Therefore I have also made you shameful and dishonorable before all the people,
Because you have not kept my ways,
but have been incomplete in the law.
Have we not all one father?
Has not only one God created us?
Why do we deal unfaithfully every man against his brother,
by disrespecting the covenant of our fathers?
 

Judah has been unfaithful,
and an abomination is committed in Israel and in Jerusalem;
because Judah has defiled the holiness of the LORD which he loved,
and has married the daughter of a strange god.
The LORD will cut off the man that does this,
the master and the scholar,
out of the tabernacles of Jacob,
and him that offers an offering to the LORD of hosts.
And this have you done again,
covering the altar of the LORD with tears,
with weeping, and with crying out,
because the LORD doesn’t regard the offering any more,
nor receives it with good will at your hand.
Still you ask, Why?
Because the LORD has been witness
between you and the wife of your youth,
against whom you have been untrue:
Still, she is your companion, and the wife of your covenant.