TRANSLATION MATTHEW 12:38
Then the legal experts and the pharisees responded to him, “Teacher, we want to see a sign from you.”
In answer Jesus said to them.”A bad and idolatrous brood demands a sign, and it will not be given a sign unless it is the sign of the prophet Jonah, for just as Jonah spent three days and three nights in the whale’s belly, so the Son of Man will spend three days and three nights in the heart of the earth. The people of Nineveh will stand in condemnation of this brood at the Judgement. because they changed their minds at Jonah’s preaching and see this! something greater than Jonah is here. The Queen of the South will rise up at the Judgement with this brood and will condemn it because she came from the ends of the earth to listen to Solomon, and see this! something greater than Solomon is here.
When Jesus talked about “broods” or “Generations” he could be justly accused of sweeping generalisations. Obviously within the Jewish brood of his own time were many people who were neither bad nor idolatrous. It was part of prophetic speech in his tradition to denounce the whole nation for the attitudes of its ruling classes.
In this case the religious leaders demand that Jesus give them some sign that he is a prophet or in some way authorised by God to teach the people. Jesus offers only the sign of Jonah, the prophet who unwillingly preached to the citizens of Nineveh, who listened and changed their minds. Jesus suggests that his mission is to arouse a national change of mind. But before Jonah preached he spent time in the whale’s belly. Jesus suggests that if he plays the role of Jonah he may need also to spend time ‘in the heart of the earth’ Doubtless this teaching has become mixed up with the story of Jesus’ death and resurrection, but it’s worth mentioning that the ‘three days’ is a Hebrew idiom in which the third day brings something good. Jesus may have used it in this sense.
In Jesus’ thinking the Son of Man, that is, the cooperative venture that brings God’s justice, is not immediately victorious, but must undergo defeat and obscurity.
Matthew uses this material to assert Jesus’ prophetic mission, while adding the words about ‘something greater’ to suggest a definitive event of God’s rescue and judgement. It is someTHING not someONE greater: the language refers to a divine event. Again Matthew shows Jesus quarrying material from his tradition of faith, and using it to point to his own uniqueness.
I like this. The sign of Jonah is almost always taken to refer to the burial and resurrection of Christ. But here it seems you have the right interpretation.