1 If, on behalf of error and inexcusable dissension, and falsehoods which have been in every way possible disproved, men are so presumptuous as to persevere in boldly assailing and threatening the Catholic Church, which seeks their salvation, how much more is it reasonable and right for those who maintain the truth of Christian peace and unity,— truth which commends itself even to those who profess to deny it or attempt to resist it—to labour constantly and with energy, not only in the defence of those who are already Catholics, but also for the correction of those who are not yet within the Church! For if obstinacy aims at the possession and exercise of indomitable strength, how great should be the strength of constancy which devotes persevering and unwearied labours to a cause which it knows to be both pleasing to God, and beyond all question necessarily approved by the judgment of wise men!
Source: Letters (New Advent)