Malachi 1:6-7

6The Lord Almighty says this to the priests: ‘A son respects his father. A servant respects his master. If I am really your father and your master, why do you not respect me? You are my priests, but you insult my name. But then you ask, “What have we done to insult your name?”

7You insult my name when you offer unclean sacrifices to me on my altar. But you ask, “How have we offered unclean sacrifices to you?” You have shown that you do not respect the Lord's altar as important.