Luke"s reference to the crowds increasing ties this verse in with the previous incident involving the criticism of His miracles ( Luke 11:14-26). Jonah himself was the sign of impending judgment to the Ninevites. His supernatural appearance and preaching triggered widespread repentance. Likewise the supernatural appearance and preaching of Jesus and the repentance that accompanied it signified impending judgment. The difference was that the positive response to Jonah"s ministry, by Gentiles no less, postponed God"s judgment. The negative response to Jesus" ministry did nothing to postpone God"s judgment on Israel. This judgment consisted of the postponement of the kingdom and the destruction of Jerusalem. The rejection of Jesus" preaching was even more serious because miracles accompanied it. The title "Son of Man" presents Jesus as superior to Jonah. [source][source][source]
Luke did not mention Jesus" reference to Jonah"s three days and nights in the great fish, though that would be a sign that Jesus had come from God after the Resurrection (cf. Matthew 12:40). [source][source][source]