Charles Ellicott Commentary Jonah 1:17

"And Jehovah prepared a great fish to swallow up Jonah; and Jonah was in the belly of the fish three days and three nights." — Jonah 1:17 (ASV)

Now the Lord. —In the Hebrew,Jonah 2:0 commences with this verse.

Had prepared.— The pluperfect is misleading. Understand it as appointed, and compare Jonah 4:6-8, where the same word is used of the gourd, the worm, and the east wind. The Authorized Version renders the word accurately in Job 7:3; Daniel 1:5–10. Previous special preparation is not implied, still less creation for the particular purpose. God employs existing agents to do His bidding.

A great fish. —The Hebrew dag is derived from the prolific character of fish, and a great fish might stand for any one of the sea monsters. The notion that it was a whale rests on the Septuagint and Matthew 12:40. But κῆτος was a term for any large fish, such as dolphins, sharks, etc. (See Homer's Odyssey 12.97.)

And unless we have previously determined the question of whether the sacred writer intended the Book of Jonah to be a literal history, an apologue founded on history, or a pure and simple parable, tota hœc de pisce Jonœ disquisitio, as an old commentator observes, vana videtur atque inutilis.

The explanations given by commentators are divided into those of a strictly preternatural kind (for instance, that a fish was created for the occasion) and those of a natural or semi-natural kind (for instance, that it was a ship, an inn bearing the sign of the whale, or a white shark. For this last hypothesis, see all that can be collected in Dr. Pusey’s commentary on Jonah).

In early Christian paintings, the monster appears as a huge dragon.

Three days and three nights. —See Matthew 12:40, New Testament Commentary.