How did the LORD answer David's offerings on Ornan's threshing floor?

Answer: With fire from heaven

David built an altar and called on the LORD, who answered him with fire from heaven on the altar of burnt offering.

“And there he built an altar to the LORD and offered burnt offerings and peace offerings. He called upon the LORD, who answered him with fire from heaven on the altar of burnt offering.”— 1 Chronicles 21:26 (BSB)