4 As We direct our thoughts, on the one hand, to the countless multitudes of Our sons who have a share in the blessings of divine faith, especially in countries that have long since become Christian, and on the other hand as We consider the far more numerous throngs of those who are still waiting for the day of salvation to be announced to them, We are filled with a great desire to exhort you again and again, Venerable Brethren, to support with zealous interest the most holy cause of bringing the Church of God to all the world. May it come to pass that Our admonitions will arouse a keener interest in the missionary apostolate among your priests and through them set the hearts of the faithful on fire!
Source: Fidei Donum (Vatican.va)