What does Acts 27:23 mean?

Paul is encouraging his 275 fellow crew members and passengers (Acts 27:37), all of whom are convinced they're going to die in the middle of the Mediterranean Sea. Their ship is enveloped by a storm so strong they haven't seen the sun in days. Nearby is the Syrtis: a large gulf riddled with hidden reefs. The crew has already tossed some of the cargo and ship's tackle into the water to try to raise the ship higher in the water and slow it down (Acts 27:17–20).

Paul had told the ship's captain and pilot that if they left the protection of Crete they would lose the ship, the cargo, and their lives (Acts 27:9–10). Paul has apparently spent the past few days praying that his prediction—presumably based on extensive first-hand experience (2 Corinthians 11:25)—would not come true. In response, God sends an angel to let him know: the ship and cargo will be lost, but not the lives of the people (Acts 27:24).

Jonah can be considered a foil for Paul (Jonah 1). Jonah was a passenger on a ship in a fierce storm in the Mediterranean (Jonah 1:4); Paul is, too. Jonah was running from God's call on his life to warn his nation's enemies to repent or face destruction (Jonah 1:1–3); Paul is running toward God's call to warn his nation's enemies to repent or face eternal destruction (Acts 23:11). Jonah saved lives by insisting the crew throw him overboard so the storm would stop (Jonah 1:12); Paul saves lives by warning the centurion that the crew is about to go overboard and abandon them (Acts 27:30–32). Jonah was safely spit up by a whale (Jonah 2:10); Paul is spit up by the storm, along with all the other survivors (Acts 27:43–44). Both faced many hardships on their way to fulfilling God's call on their lives. The main difference is that Paul did so willingly.