Matt 12:38 Then certain of the scribes and of the Pharisees answered, saying, Master, we would see a sign from thee. 39 But he answered and said unto them, An evil and adulterous generation seeketh after a sign; and there shall no sign be given to it, but the sign of the prophet Jonas: 40 For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.
After Jonah came out of the whale, he obeyed the call to preach repentance, and the whole city turned to God.
Jesus preached repentance before He died, finishing Luke 13:34
What were those (who had asked Jesus for a sign) supposed to deduce from His three days in 'the heart of the earth'?
Was it simply Luke 16:31 ?