Letters 94.21

“But,” comes the reply, “error is the source of sin; precepts do not remove error, nor do they rout our false opinions on the subject of Good and Evil.” I admit that precepts alone are not effective in overthrowing the mind’s mistaken beliefs; but they do not on that account fail to be of service when they accompany other measures also. In the first place, they refresh the memory; in the second place, when sorted into their proper classes, the matters which showed themselves in a jumbled mass when considered as a whole, can be considered in this with greater care. According to our opponents theory, you might even say that consolation, and exhortation were superfluous. Yet they are not superfluous; neither, therefore, is counsel.

Seneca, Letters to Lucilius 94.21, translated by Richard Mott Gummere