It is wonderful, but it is too well vouched to admit of a doubt, that by the powers of rhetoric you may produce in mankind almost any change more easily than this. It is not unprecedented that one should persuade a multitude, from mistaken motives of religion, to act the part of ruffians, fools, or madmen; to perpetuate the most extravagant, nay, the most flagitious actions; to steel their hearts against humanity, and the loudest calls of affection; but where is the eloquence that will gain such an ascendent over a multitude, as to persuade them, for the love of God, to be wise, and just, and good? Happy the preacher whose sermons, by the blessing of Heaven, have been instrumental in producing even a few such instances! Do but look into the annals of church history, and you will soon be convinced of the surprising difference there is in the two cases mentioned–the amazing facility of the one, and the almost impossibility of the other.
George Campbell, The Philosophy of Rhetoric