He asks, Will they revive the stones out of the heaps of rubbish, and burned ones at that?
The Babylonians had pried the stones from Jerusalem’s walls and left them where they had fallen. They had also set the city on fire. Stones superheated by the fire lose their strength and so would crumble when builders tried to reset them into the wall. With the word revive
Sanballat implies that the stones the Jews are using are functionally dead, useless for a restored wall.
To clarify, it should be noted that this charge is an embellishment of the reality. The Babylonians indeed burned the gates (made of wood), but the fires would have left most of the stones (lying on ground level) largely untouched.
2 And he said in the presence of his brothers and of the army of Samaria, “What are these feeble Jews doing? Will they restore it for themselves? Will they sacrifice? Will they finish up in a day? Will they revive the stones out of the heaps of rubbish, and burned ones at that?”