Adam Clarke on Acts 27:23

The - God, whose I am, and whom I serve - This Divine communication was intended to give credit to the apostle and to his doctrine; and, in such perilous circumstances, to speak so confidently, when every appearance was against him, argued the fullest persuasion of the truth of what he spoke; and the fulfillment, so exactly coinciding with the prediction, must have shown these heathens that the God whom Paul served must be widely different from theirs.