3 When, in Our time, people desire to attempt difficult enterprises with the united counsel and strength of several persons, we have seen societies everywhere established, of which some have been formed for this very purpose, viz., to serve for the propagating of religion in certain countries. Amongst others shines forth the pious association founded about sixty years ago at Lyons, in France, which has taken the name of the Propagation of the Faith. Its first object was to carry assistance to certain missions in America: soon, like the grain of mustard seed, it grew to a large tree, whose umbrageous branches spread far and wide, so that it affords effectual help to all missions all over the earth. This grand institution was promptly approved by the Pastors of the Church, and has been honoured by abundant laudatory testimonials. The Roman Pontiffs Pius VII, Leo XII, Pius VIII, Our Predecessors, both strongly commended it and enriched it with the gifts of Indulgences. And Gregory XVI. still more warmly favoured it and embraced it in the fullness of his paternal charity, since he, in his Encyclical Letters dated the 15th day of August, in the 40th year of this century, spoke of the same in these terms.: "We judge to be most worthy of the admiration and love of all good men this truly great and most holy work, which by modest offerings and daily prayers addressed by each associate to God is sustained, increased and grows strong, and which is occupied in maintaining Apostolic labourers and in exercising works of Christian charity towards neophytes, as well as in delivering the faithful from the attack of persecutions. Nor must we think that it is without a peculiar design of Divine Providence that an institution of so much advantage and utility to the Church has in these latter times been vouchsafed to her. For whilst all kinds of machinations of the infernal enemy harrass the beloved spouse of Christ, nothing could have happened more opportunely for her than that the faithful, influenced by a desire of propagating Catholic truth, should with united zeal and collected strength endeavour to gain all men to Christ." With this preface he exhorted the Bishops to apply themselves with diligence, each in his own diocese, so that so salutary an institution might daily grow and increase. Nor did Pius IX., of glorious memory, depart from the footsteps of his Predecessor, seeing that he allowed no opportunity to pass by of assisting this most deserving society, and of promoting its prosperity. Indeed, by his authority more ample privileges of Pontifical Indulgence were granted to the associates, the piety of Christians was excited to the sustaining of its work, and the most eminent among the associates, whose special merits were manifest, were decorated with various insignia of honour; finally certain external aids which accrued to this institution were by the same Pontiff honoured with praise and approval.
Source: Sancta Dei Civitas (Vatican.va)