1 Corinthians 2:5
But while we say these things without intermission, over and over, they occur very seldom. Howbeit, be they done or not, it is right to remind you of them continually. For if some are engaged in deceiving by their fair speech, so much more is it the duty of those who allure back unto the truth, not to grow weary of speaking what is profitable. Again: if the deceivers make use of so many contrivances— spending as they do money, and applying arguments, and undergoing dangers, and making a parade of their patronage— much more should we, who are winning men from deceit, endure both dangers and deaths, and all things; that we may both gain ourselves and others, and become to our enemies irresistible, and so obtain the promised blessings, through the grace and loving-kindness, etc.
Source: Homilies on First Corinthians (New Advent)