“burden.” The word of the Lord can be a burden to the prophet, and then, when it is spoken, can be a burden to the people. It might have been more clear in English to say “burdensome message” instead of “burden,” but the Hebrew word is “burden.”
[For more information on “burden,” see commentary on Malachi 1:1.]
“idols.” The Hebrew text has the word 'eliyl (#0457 אֱלִיל), more literally “Worthless Ones” or “worthless things,” a sarcastic name for “idols” (see commentary on Hab. 2:18, “Worthless Ones”).