First, it may not have been a whale, the word is a great fish which means it was one of considerable size. Also we find that God appointed this fish to swallow Jonah, as he appointed many other things of his creation that are recorded in the book of Jonah.

Many people believe that Jonah stayed alive in the fish for three days and that is the miracle but this is not what the Scripture portrays of this event.

It says he cried from “Out of the belly of Sheol” not just the whales belly. The Hebrew word for belly of Sheol is different than the belly of the fish, indicating two different areas

The waters surrounded him even to his soul. This is an expression implying death (Ps.69:1. Jer.4:10) the deep closed, weeds wrapped around my head. His body sank to the moorings of the Mountains, where they begin (under land level). Showing he sank to the bottom before he was swallowed by the fish- which implies He died.

While his soul went too the place of the dead, the fish comes and swallows up his body and it is preserved it for 3 days.

The Bible says “The earth with its bars closed behind me forever.”  This is Old Testament language for sheol, the place of the dead. Job.38:17: “Have the gates of death been revealed to you? Or have you seen the doors of the shadow of death?

Isa 38:10 I said, "In the prime of my life I shall go to the gates of Sheol; I am deprived of the remainder of my years." Ps. 9:13 also mentions the gates of death. Sheol is the place of departed spirits the only way to get there is to die. Jonah is crying from the righteous portion of Sheol which is Abraham’s bosom, (paradise) His soul went to Sheol while his body was swallowed in the fish preserved in its belly (abdomen). He recalls his last thoughts, When My soul fainted within me, that is a description of losing consciousness. He prayed before he died, then his body was scooped up and preserved in the whale for 3 days and nights.

This is why Jesus stated : For as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth. The men of Nineveh will rise up in the judgment with this generation and condemn it, because they repented at the preaching of Jonah; and indeed a greater than Jonah is here.” (Matthew 12:40-41)

Luke 11:29-30:“This is an evil generation. It seeks a sign, and no sign will be given to it except the sign of Jonah the prophet. For as Jonah became a sign to the Ninevites, so also the Son of Man will be to this generation.”

The sign Jesus is speaking of is his last to the unbelievers- His resurrection.

The point Jesus is making is that Jonah was dead not alive for three days in the fish. If Jonah did not die than neither did Jesus because he is using him as a example of a miracle for his resurrection. If Jonah did not die than Jesus’ did not either.