37 But since the People of God lives in communities, especially in dioceses and parishes, and becomes somehow visible in them, it is also up to these to witness Christ before the nations. The grace of renewal cannot grow in communities unless each of these extends the range of its charity to the ends of the earth, and devotes the same care to those afar off as it does to those who are its own members. Thus the whole community prays, works together, and exercises its activity among the nations through those of its sons whom God has chosen for this most excellent task. It will be very useful, provided the universal scope of mission work is not thereby neglected, to keep in contact with missionaries who are from one's own community, or with some parish or diocese in the missions, so that the communion between the communities may be made visible, and serve for their mutual edification.
Source: Ad Gentes (Vatican.va)