For, behold, the day cometh, that shall burn as an oven; and all the proud, yea, and all that do wickedly, shall be stubble: and the day that cometh shall burn them up, saith the LORD of hosts, that it shall leave them neither root nor branch. Behold, the day cometh, that shall burn as an oven - The destruction of Jerusalem by the Romans.
And all the proud - This is in reference to Malachi 3:15 of the preceding chapter.
The day that cometh shall burn them up - Either by famine, by sword, or by captivity. All those rebels shall be destroyed.
It shall leave them neither root nor branch - A proverbial expression for total destruction. Neither man nor child shall escape.