Pleo (πλέω) means to sail, to voyage by ship, or to navigate. It is the basic Greek verb for sea travel, which was the primary mode of long-distance transportation in the ancient Mediterranean. Paul's missionary journeys depended heavily on sailing.
Sailing in the ancient world was dangerous — ships were small, weather unpredictable, and navigation primitive. Paul's sea voyages illustrate both his missionary zeal and trust in God's providence. In Acts 27, Paul's voyage to Rome includes a dramatic shipwreck demonstrating God's faithfulness in catastrophe. Luke records numerous instances of pleo throughout Acts as Paul crisscrosses the Mediterranean. Paul faced shipwreck three times (2 Corinthians 11:25), yet kept sailing because the mission demanded it. The seas that threatened his life also served as highways by which the gospel reached the nations.