Repeat these passages to your opponents, and if they are convinced, praise the good Lord for that, by means of your zeal, He has benefited them. If they remain unconvinced, enter into no discussion with them about doctrines, for it is forbidden by the divine apostle to “strive about words to no profit but to the subverting of the hearers.” But do you keep inviolate the teaching of the Gospels, that in the day of His appearing you may bring to the righteous Judge what has been entrusted to you with its due interest, and may hear the longed for words “Well done good and faithful servant; you have been faithful over a few things I will make you ruler over many things. Enter thou into the joy of your Lord.”
Source: Letters (New Advent)