This is a command to priests, and the first thing it asks for fits inside a heart: 2"if you will not take it to heart to give honor to my name." The trouble is located exactly there. God adds 2"I have already cursed them, because you do not lay it to heart." The priests are still working and the altar is still lit. What is missing is the heart that would honor the name they serve.
God names the punishment in the most humiliating terms available: 3"spread dung on your faces, the dung of your offerings." The waste of the sacrifices was burned outside the camp because it was unfit for the altar (Leviticus 4:11-12). The priests had treated God's table as cheap in chapter 1, and now the refuse of what they offered lands on their own faces. A priest who treats the holy as ordinary ends up ordinary himself.
Then God remembers: 5"My covenant with him was one of life and peace, and I gave them to him." No single passage records a covenant with Levi by that name. Malachi gathers what Scripture says about Levi's zeal after the golden calf (Exodus 32:26-29), about Phinehas and the covenant of peace (Numbers 25:12), and about Moses' blessing on the tribe (Deuteronomy 33:8-10). God gave life and peace, and Levi gave back awe.
Then comes the portrait, one of the fullest of a priest in the Old Testament: 6"True instruction was in his mouth, and no wrong was found on his lips." The word instruction appears in each of verses 6 to 9, and it is torah. The priest's lips guard it (verse 7). The word for messenger is the same word inside the prophet's name, Malachi, and behind the promise of 3:1. A priest is God's messenger, and his mouth is where people go to find out what God said.
Then the mirror. These priests turned aside from the way and caused many to stumble by their instruction (verse 8). Set the portraits side by side. Levi turned many from iniquity, and these priests caused many to stumble. Levi walked with God, and they turned aside from the way. A teacher's power to move many works in either direction. The specific failure is in verse 9: they show partiality in their instruction. They shaded the torah to please the hearer, and the result is contempt, since people eventually see through a teacher who says what they want to hear.
The New Testament opens with a priest. Luke calls Zechariah righteous before God, and the angel says his son will turn many of the children of Israel to the Lord their God (Luke 1:6, 16). That is Levi's job description from Malachi 2:6. Only one person fills it without a flaw. Peter says of Jesus that no deceit was found in his mouth (1 Peter 2:22), and Hebrews says he holds his priesthood permanently and always lives to make intercession for us (Hebrews 7:24-25).
That leaves those of us who teach, and the word covers more people than it first seems to: a father explaining why we pray, a grandmother reading a Bible story, a friend answering a question about God. People seek instruction from the mouths near them. The temptation named here is partiality, bending what God said until it stops weighing on the listener. The remedy is the phrase from verse 2, lay it to heart. Guarding a word begins in the one who holds it.
Prayer
Father, make us people who lay your words to heart before we lay them on anyone else. Forgive us for shading what you said so that it would weigh less on the person in front of us, and for handling holy things as though they were ordinary. Thank you for Christ, the priest whose lips guarded every word and whose covenant gives life and peace. In his name, amen.