Albert Barnes Commentary Acts 26:24

"And as he thus made his defense, Festus saith with a loud voice, Paul, thou art mad; thy much learning is turning thee mad." — Acts 26:24 (ASV)

Festus said with a loud voice, amazed at the zeal and fervor of Paul. Paul undoubtedly showed deep interest in the subject and great earnestness in the delivery of his defense.

Thou art beside thyself. You are deranged; you are insane. The reasons why Festus thought Paul mad were probably:

1. His great earnestness and excitement on the subject.
2. His laying such stress on the gospel of the despised Jesus of Nazareth, as if it were a matter of infinite importance. Festus despised it, and he regarded it as proof of derangement that so much importance was attached to it.
3. Festus regarded, probably, the whole story of the vision that Paul said had appeared to him as the effect of an inflamed and excited imagination, and as proof of delirium.

This is not an uncommon charge against Christians, especially when they show any unusual zeal.

Sinners regard them as under the influence of delirium and fanaticism, as terrified by imaginary and superstitious fears, or as misguided by fanatical leaders.

Husbands often think their wives deranged in this way, parents their children, and wicked men the ministers of the gospel.

The lighthearted think it proof of derangement that others are serious, anxious, and prayerful; the rich, that others are willing to part with their property to do good; the ambitious and worldly, that others are willing to leave their country and home to go among the Gentiles to spend their lives in making known the unsearchable riches of Christ.

The truly sober and rational people of the world—those who fear God and keep His commandments, who believe that eternity is before them and who strive to live for it—are thus charged with insanity by those who are really deluded and who are living lives of madness and folly.

The inhabitants of a madhouse often think all others deranged but themselves; but there is no madness so great, no delirium so awful, as to neglect the eternal interests of the soul for the sake of the poor pleasures and honors this life can give.

Much learning doth make thee mad. It is probable that Festus was acquainted with the fact that Paul had been well instructed and was a learned man. Paul had not, while before him, particularly shown his learning. But Festus, acquainted in some way with the fact that he was well educated, supposed that his mind had been unsettled, and that the effect of it was seen in devotion to a fanatical form of religion. The tendency of long-continued and intense application to produce mental derangement is everywhere known.

Doth make thee mad. This phrase means it impels, drives, or excites you (peritrepei) to madness.

Note also the phrases "spoke for himself" and "Made his defense." Regarding make thee mad, see 2 Kings 9:11.