Sancta Dei Civitas §8

⁸ In the meanwhile new routes have been opened, in consequence of more complete exploration of places and populations, towards countries hitherto accounted impracticable; numerous expeditions of the soldiers of Christ have been formed, and new stations have been established; and thus many labourers are now wanted to devote themselves to these missions, and contribute seasonable help. We pass over in silence the difficulties and obstacles arising from contradictions. For it often occurs that deceivers, sowing error, simulate the Apostles of Christ, and, being abundantly furnished with human resources, interfere with the ministry of Catholic priests, or creep in after their departure, or raise pulpit against pulpit, thinking it sufficient to render the way of salvation doubtful to the persons who hear the word of God interpreted in different ways. Would that their artifices had no success! This is certainly to be regretted, that even those who are disgusted with such teachers, or have never met with them, and who desire the pure light of truth, should often have no man at hand to instruct them in wholesome doctrine and to bring them into the bosom of the Church.