51 Everybody knows how the mutual assistance which is exchanged among Catholic organizations established all over the world can be—as Our predecessor Pius XII has pointed out—of great use and much value to the apostolate of the laity in mission territories. On the educational plane, these organizations can help by devising Christian solutions to current problems, especially social problems, in the newly established nations; on the apostolic plane, they can help by recruiting and organizing a body of laymen, willing to serve under Christ's banner. We know that this has been done, and is being done, by lay missionaries who chose to leave their countries, either temporarily or for life, in order to contribute, by manifold activities, to the social and religious welfare of mission countries. Let us pray fervently to God that the numbers of these generous Christians be multiplied, and that God's support will never be absent in their difficulties and labors, which they are meeting with truly apostolic spirit. The Secular Institutes will be able to give the local laity in mission territories generous and loyal help, if, by their example, they attract imitators, and if they place their talents and work, promptly and willingly, at the disposal of the local ordinaries, in order to speed the growing-up process of the new Christian communities.
Source: Princeps Pastorum (Vatican.va)