I found this email and I think it will explain this parable really well.
http://bible-truths.com/email6.htm#three ---------
Jesus Christ ALWAYS, ALWAYS spoke to the multitudes in public in PARABLES. Parables are not LITERAL, neither do they lie. I neglected to treat this teaching of Jesus as a "parable."
It NOWHERE SAYS that Jesus would be "DEAD for three days and three nights." I just ASSUMED that is what was meant by the phrase "in the HEART OF THE EARTH."
I'll just give you the gist of the answer, as my time is limited right now. Jesus called "three days and three nights in the HEART OF THE EARTH," "the SIGN of Jonah." Now then, if Christ was to be DEAD for the exact period of TIME of three days and three nights, How then could that be "the sign of Jonah?" JONAH WAS NOT DEAD AT ALL!!! Jonah went through 'A LIVING HELL' if you will! Besides, Jesus was NOT buried in the "HEART" of the earth, He was buried in an ABOVE THE EARTH TOMB! Maybe twenty inches or so on the other side of a big stone.
"In the HEART OF THE EARTH" is a parable showing the unbelievable agony of the human spirit and flesh that Jesus would go through LEADING UP TO and INCLUDING the time in the tomb. And those three days began on the PREPARATION FOR THE PASSOVER, seeing that Jesus, HIMSELF, was to BE THE PASSOVER!!!
And don't forget the AGONY IN THE GARDEN when Jesus SWEAT BLOOD!! No one will ever know what torture He endured those "three days and three nights in the HEART OF THE EARTH." BEFORE the beatings and crucifixion we read this:
"NOW is My SOUL TROUBLED [Greek: DISTRESSED, IN TURMOIL!]; and what shall I say? Father, save Me from this hour: but for his cause came I unto THIS HOUR" (John 123:27).
The "heart of the earth" is the very DEPTH OF THE FLESH. The flesh of man is "of the EARTH, EARTHY" Paul tells us.
Again, thank you for your keen observation.
God be with you,
Ray