William Burkitt on 2 Corinthians 5:13

The holy apostle was sometimes so zealously transported and carried forth in his high actings for Jesus Christ, that the false apostles represented him as a frantic person, crazy, mad, and what not; "Be it so, (says the holy man,) it is unto God, in his cause, and to propagate his glory, and not my own: or if I be sober in my words and actions, it is for your benefit, not my own."

Learn hence, That wicked and carnal men account and represent the holy servants of God as a sort of madmen. Workings of grace are sometimes so far above reason, that they seem to be without reason: there are several acts of holiness, which the profane world esteem as madness; as eminent self-denial, great seriousness in religion, their burning zeal, their holy singularity, their fervours of devotion, their patience and meekness under sufferings and reproaches. All these acts of holiness represent the saints as madmen to carnal men.