Adam Clarke on Acts 26:25

I am not mad, most noble Festus - This most sensible, appropriate, and modest answer, was the fullest proof he could give of his sound sense and discretion. The title, ΚρατιϚε, most noble, or most excellent, which he gives to Festus, shows at once that he was far above indulging any sentiment of anger or displeasure at Festus, though he had called him a madman; and it shows farther that, with the strictest conscientiousness, even an apostle may give titles of respect to men in power, which taken literally, imply much more than the persons deserve to whom they are applied. ΚρατιϚος, which implies most excellent, was merely a title which belonged to the office of Festus. St. Paul hereby acknowledges him as the governor; while, perhaps, moral excellence of any kind could with no propriety be attributed to him.

Speak forth the words of truth and soberness - Αληθειας και σωφροσυνης, Words of truth and of mental soundness. The very terms used by the apostle would at once convince Festus that he was mistaken. The σωφροσυνη of the apostle was elegantly opposed to the μανια of the governor: the one signifying mental derangement, the other mental sanity. Never was an answer, on the spur of the moment, more happily conceived.