A.T. Robertson Commentary Acts 27:25

"Wherefore, sirs, be of good cheer: for I believe God, that it shall be even so as it hath been spoken unto me." — Acts 27:25 (ASV)

Wherefore be of good cheer (διο ευθυμειτε). God had spoken. That was enough. This old verb from ευθυμος in the N.T. only here, verse 25; James 5:13. See the adjective 27:36.

For I believe God (πιστευω γαρ τω θεω). This is Paul's reason for his own good cheer and for his exhortation to confidence in spite of circumstances so untoward. Paul had doubtless prayed for his own life and for the lives of all. He was sure that he was to bear his witness in Rome.