Commentary of Charles Spurgeon, Adam Clarke & Matthew Henry
And when this people, or the prophet, or a priest, shall ask thee, saying, What is the burden of the LORD?
thou shalt then say unto them, What burden?
I will even forsake you, saith the LORD. 
And as for the prophet, and the priest, and the people, that shall say, The burden of the LORD, I will even punish that man and his house.
Thus shall ye say every one to his neighbor, and every one to his
brother, What hath the LORD answered? and, What hath the LORD spoken?
And the burden of the LORD shall ye mention no more: for every man's
word shall be his burden; for ye have perverted the words of the living
God, of the LORD of hosts our God.
Thus shalt thou say to the prophet, What hath the LORD answered thee? and, What hath the LORD spoken? But since ye say, The burden of the LORD; therefore thus saith the LORD;
Because ye say this word, The burden of the LORD, and I have sent unto
you, saying, Ye shall not say, The burden of the LORD;
Therefore, behold, I, even I, will utterly forget you, and I will forsake you, and the city that I gave you and your fathers, and cast you out of my presence: And I will bring an everlasting reproach upon you, and a perpetual shame, which shall not be forgotten.
Vs. 33-40
The profaneness of the people, with that of the priests and
prophets, is here reproved in a particular instance, which may seem of small
moment in comparison of their greater crimes; but profaneness in common
discourse, and the debauching of the language of a nation, being a notorious
evidence of the prevalency of wickedness in it, we are not to think it strange
that this matter was so largely and warmly insisted upon here.
---The sin here charged upon them is bantering God's prophets
and dialect they used, and jesting with sacred things. They asked,...What is the burden of the Lord? — The word משא massa, here used, 
signifies burden, oracle, prophetic discourse; ..... But the persons in the text appear to have been mockers. "Where is this burden of the Lord?"-"What is the burden now?" To this insolent question the prophet answers in the following I will even forsake you — I will punish the prophet, the priest and the people, that speak thus.
---They make the word of God a burden to themselves, and then quarrel with the
ministers for making it a burden to them.
Thus the scoffers of the latter days,
while they slight heaven and salvation, reproach faithful ministers for
preaching damnation. ....God takes notice of, and is much displeased
with, those who burlesque sacred things, and who, that they may make a jest of
scripture truths and laws, put jests upon scripture language....You shall not mention the burden of
the Lord any more in this profane careless manner.....God had taken them to be a people
near to him; but they shall now be cast out of his presence. They had
been great and honorable among the nations; but now God will bring upon them an
everlasting reproach and a perpetual shame.
Both their sin and
their punishment shall be their lasting disgrace. It is here upon record, to
their infamy, and will remain so to the world's end. .... God's word will
be magnified and made honorable when those that mock at it shall be vilified
and made contemptible. Those that despise me shall be lightly esteemed.
The word of the Lord cannot fail.
