Direct thine own intention aright then, and thou shalt never receive harm from any, but shall get the greatest gain, not only from the good but even from the wicked. For on this account, as I have before said, God has suffered men to be with one another, and especially the wicked with the good, in order that they may bring them over to their own virtue. Hear at least what Christ saith to his disciples, “The Kingdom of heaven is like unto a woman who took leaven and hid it in three measures of meal.” So that the righteous have the power of leaven, in order that they may transfer the wicked to their own manner of conduct. But the righteous are few, for the leaven is small. But the smallness in no way injures the lump, but that little quantity converts the whole of the meal to itself by means of the power inherent in it. So accordingly the power also of the righteous has its force not in the magnitude of their number, but in the grace of the Spirit. There were twelve Apostles. Dost thou see how little is the leaven? The whole world was in unbelief. Dost thou see how great is the lump? But those twelve turned the whole world to themselves.
St. John Chrysostom, Three Homilies Concerning the Power of Demons, Homily III