John Calvin Commentary Acts 25:9

"But Festus, desiring to gain favor with the Jews, answered Paul and said, Wilt thou go up to Jerusalem, and there be judged of these things before me?" — Acts 25:9 (ASV)

And Festus. Whether Festus knew something of their ambush (which we may well conjecture) or whether he was altogether ignorant of it, he deals unjustly with Paul; and we see how quickly those who are not guided by the Spirit of God are drawn into all corruption. For Festus does not openly despise or hate Paul; but ambition, and perhaps also desire for gain, prevailed, so that, to please the other party, he unjustly brings him into danger of death. Also, it is likely that he was enticed with the smell (that is, the hope) of some reward to listen so courteously to the priests.

Nevertheless, I marvel that he gives Paul leave to choose, and does not rather, according to his authority, command them to take him whether he wanted to or not. Surely, we gather that he was held back by fear, for fear that he might infringe the privilege of the city of Rome, which was a very detestable crime. Nevertheless, he craftily sought to persuade Paul not to refuse to be judged at Jerusalem. For he was not ignorant of what indeed came to pass: that a Roman citizen could lawfully appeal, so that he (Festus) could then proceed no further. Nevertheless, he deserved no thanks that Paul was not delivered into the hands of murderers.