Acts 23:11
And the night following the Lord stood by him, and said, Be of good cheer, Paul: for as thou hast testified of me in Jerusalem, so must thou bear witness also at Rome. And the night following the Lord stood by him, and said, Be of good cheer, Paul: for as thou hast testified of me in Jerusalem, so must thou bear witness also at Rome.
On the night following his testimony in Jerusalem, while he was confined in the fortress, the Lord stood by Paul to encourage him. He came to Paul in a night vision in answer to earnest prayer when Paul was discouraged and uncertain whether his work in Jerusalem had pleased God. The Lord affirmed that Paul had truly testified of Him in Jerusalem. He declared that as Paul had testified there, so he must also bear witness at Rome.
The promise meant that Paul's imprisonment did not end his work. He would reach Rome and there witness for Christ. He would go to Rome as a prisoner, though he did not yet know he would go in that way.
That assurance that he would be preserved to witness in Rome gave Paul confidence during the later storm at sea. Trusting the promise, he had no fear for his own life but relied on God, knowing God would preserve him to testify in Rome. On the strength of that same promise he also pleaded for the lives of all who sailed with him, and God revealed to him that his prayer for them was granted.