Malachi 1:1

The prophecy of this book is entitled, The burden of the word of the Lord (Mal 1:1), which intimates, 1. That it was of great weight and importance; what the false prophets said was light as the chaff, what the true prophets said was ponderous as the wheat, Jer 23:28. 2. That it ought to be often repeated to them and by them, as the burden of a song. 3. That there were those to whom it was a burden and a reproach; they were weary of it, and found themselves so aggrieved by it that they were not able to bear it. 4. That to them it would prove a burden indeed, to sink them to the lowest hell, unless they repented. 5. That to those who loved it and embraced it, and bade it welcome, though it was a light burden, as our Saviour calls it (Mat 11:30), yet it was a burden. This burden of the word of the Lord was sent, 1. To Israel, for to them pertained the lively oracles of prophecy as well as those of the written word. Many prophets God had sent to Israel, and now he will try them with one more. 2. By Malachi, by the hand of Malachi, as if it were not a message by word of mouth, but a letter put into his hand, for the greater certainty.

— Matthew Henry's Concise Commentary (public domain)