33 The fact that there is a diversity of activities in the Church's one mission is not intrinsic to that mission, but arises from the variety of circumstances in which that mission is carried out. Looking at today's world from the viewppoint of evangelization, we can distinguish three situations . First, there is the situation which the Church's missionary activity addresses: peoples, groups, and socio-cultural contexts in which Christ and his Gospel are not known, or which lack Christian communities sufficiently mature to be able to incarnate the faith in their own environment and proclaim it to other groups. This is mission ad gentes in the proper sense of the term. Secondly, there are Christian communities with adequate and solid ecclesial structures. They are fervent in their faith and in Christian living. They bear witness to the Gospel in their surroundings and have a sense of commitment to the universal mission. In these communities the Church carries out her activity and pastoral care. Thirdly, there is an intermediate situation, particularly in countries with ancient Christian roots, and occasionally in the younger Churches as well, where entire groups of the baptized have lost a living sense of the faith, or even no longer consider themselves members of the Church, and live a life far removed from Christ and his Gospel. In this case what is needed is a "new evangelization" or a "re-evangelization."
Source: Redemptoris Missio (Vatican.va)