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. Matthew 12:40
Let's suppose you and your family were at the beach. You saw a large fish, maybe a dolphin. Maybe a whale. Your children were curious about the type of fish. Maybe they knew the story of Jonah and the whale and were wondering if the fish they saw could swallow a person. Could it swallow them?
