“Behold, is it not from Yahweh of Armies.” In other word, “Does it not come from Yahweh…?” The NET Bible has nuanced this for clarity to “The LORD who commands armies has decreed…,” while the NLT has “Has not the LORD of Heaven’s Armies promised.” Yahweh had stated over and over that people’s evil work would not last, and in this verse, God is reminding people of that fact.
“labor only to fuel the fire.” The Hebrew is more literally, “labor for the fire,” but that is unclear in English, so we nuanced it for clarity. The NET went with a much less literal reading, but it is very clear: “The nations’ efforts will go up in smoke.” All the evil work done by nations, even if it enriches them in this life, will burn up on the Day of Judgment. When the text says, “the peoples labor only to fuel the fire,” we have to know from the context that it is evil work, evil labor. This is not a general statement that people’s work on earth will not survive; good works will be rewarded while evil work will be burned up.