22 To propagate the truth of Jesus Christ is the truest function of the Church. Indeed, "it is the solemn duty of the Church to impart to... peoples, so far as possible, the outstanding blessings of her life and her teaching, from which a new social order should be derived, based on Christian principles." (42) Therefore, in mission territories, the Church takes the most generous measures to encourage social welfare projects, to support welfare work for the poor, and to assist Christian communities and the peoples concerned. Care must be taken, however, not to clutter and obstruct the apostolic work of the missions with an excessive quantity of secular projects. Economic assistance must be limited to necessary undertakings which can be easily maintained and utilized, and to projects whose organization and administration can be easily transferred to the lay men and women of the particular nation, thus allowing the missionaries to devote themselves to their task of propagating the faith, and to other pursuits aimed directly at personal sanctification and eternal salvation.
Source: Princeps Pastorum (Vatican.va)