3 As for Ourselves, Venerable Brothers, you well know that, from the beginning of Our Pontificate, We determined to leave nothing undone which might, by means of apostolic preachers, extend farther and farther the light of the Gospel and make easy for heathen nations the way unto salvation. It seems to Us that two special objectives ought to be aimed at in all missionary work, both of which are not only timely but necessary and closely connected with each other; namely, that a much larger number than heretofore of missionaries, well trained in the different fields of knowledge, be sent into the vast regions which are still deprived of the civilizing influence of the Christian religion; and secondly, that the faithful be brought to understand with what zeal, constancy in prayer, and with what generosity they too must co-operate in a work which is so holy and fruitful. This is precisely the object We had in mind when We commanded that the Vatican Missionary Exhibition be held. We thank God that many young hearts (a fact which has been called to Our attention) at the sight of these proofs of divine grace and of the nobility and greatness of the missionaries, received there the first call to the missionary life. So unbounded, too, was the admiration for the missionaries on the part of those who visited the Exhibition that We have every reason to believe that it will not be without lasting fruits for religion. That the weighty lessons which this Exhibition in its silent eloquence preached may not be forgotten, We ordered, as you perhaps know already, that a permanent museum be established wherein there may be conserved and shown to the public the more noteworthy objects exhibited at the Vatican Missionary Exhibition. This Museum will be established in our Palace of the Lateran on the very spot where, after peace had been restored to the Church, so many apostolic men celebrated for holiness of life and zeal for religion were sent forth, century after century, by Our Predecessors into regions "already white for the harvest."
Source: Rerum Ecclesiae (Vatican.va)