What was Korah's underlying error?
He introduced strange fire into the altar and sought to institute something foreign to the tabernacle worship. His premise was to bring in a practice contrary to what God had instructed, a gainsaying that led to judgment. He perished in that gainsaying.
Les explains that Korah's underlying error was a deliberate substitution of human invention for God's revealed instruction. Korah introduced strange fire into the altar and sought to institute something foreign to the tabernacle worship. Because the temple was not yet built, this was a direct violation of the worship God had prescribed. They were brought before Moses and Aaron, and the earth opened up and they were gone. The passage cites the gainsaying of Korah alongside Balaam's error and Cain's rationalization to warn against false teachers. Like Cain, who rationalized from the human side, Korah presumed God would accept what he devised. Like Balaam, these false teachers are motivated by materialism. The common thread is rationalization from the human side—sounding good but foreign to what God instructed.