John Calvin Commentary Acts 25:14

"And as they tarried there many days, Festus laid Paul`s case before the King, saying, There is a certain man left a prisoner by Felix;" — Acts 25:14 (ASV)

When many days. Therefore, when some time had passed and they lacked topics for conversation—as idle people tend to invent something to talk about—Paul was mentioned. For Luke intended to note this when he said that after many days were idly spent, Festus told the king about a certain man who was imprisoned.

And although Festus here both touches on the malice of the priests and also makes a display of wonderful fairness on his part, yet because he shortly after clears the accused party, he unknowingly condemns himself when he confesses that Paul was forced to appeal so that he might not be taken to Jerusalem.

But when Festus commends the Romans, he shows what is fitting for judges. And if nature told profane men this much—that they must not allow any favor that might oppress the guiltless—how much more must judges (who have the light of the Word of God) be careful to avoid all corruption.