Adam Clarke on Acts 25:1

Now when Festus was come into the province - By the province is meant Judea; for, after the death of Herod Agrippa, Claudius thought it imprudent to trust the government in the hands of his son Agrippa, who was then but seventeen years of age; therefore Cuspius Fadus was sent to be procurator. And when afterwards Claudius had given to Agrippa the tetrarchate of Philip, that of Batanea and Abila, he nevertheless kept the province of Judea more immediately in his own hands, and governed it by procurators sent from Rome. Joseph. Ant. lib. xx. cap. 7, sec. 1. Felix being removed, Porcius Festus is sent in his place; and having come to Caesarea, where the Roman governor generally had his residence, after he had tarried three days, he went up to Jerusalem, to acquaint himself with the nature and complexion of the ecclesiastical government of the Jews; no doubt, for the purpose of the better administration of justice among them.