Albert Barnes Commentary Acts 23:11

"And the night following the Lord stood by him, and said, Be of good cheer: for as thou hast testified concerning me at Jerusalem, so must thou bear witness also at Rome." — Acts 23:11 (ASV)

The Lord stood by him. Evidently the Lord Jesus. See the comments on Acts 1:24.

Compare to Acts 22:18. The appearance of the Lord in this case was a proof that he approved the course which Paul had taken before the Sanhedrin.

Be of good cheer. It would not be remarkable if Paul, by these constant persecutions, should be somewhat dejected in mind. The issue of the whole matter was still doubtful.

In these circumstances, it must have been peculiarly consoling to him to hear these words of encouragement from the Lord Jesus, and this assurance that the object of his desires would be granted, and that he would be permitted to bear the same witness of him in Rome. Nothing else can comfort and sustain the soul in trials and persecutions, but evidence of the approval of God and the promises of his gracious aid.

Bear witness also at Rome. This had been the object of his earnest wish (Romans 1:10; Romans 15:23–24), and this promise of the Lord Jesus was fulfilled (Acts 28:30–31). The promise which was here made to Paul was not directly one of deliverance from the present persecution, but it implied that, and made it certain.