17 There is a very urgent need for this individual apostolate in those regions where the freedom of the Church is seriously infringed. In these trying circumstances, the laity do what they can to take the place of priests, risking their freedom and sometimes their life to teach Christian doctrine to those around them, training them in a religious way of life and a Catholic way of thinking, leading them to receive the sacraments frequently and developing in them piety, especially Eucharistic devotion. While the sacred synod heartily thanks God for continuing also in our times to raise up lay persons of heroic fortitude in the midst of persecutions, it embrace them with fatherly affection and gratitude. The individual apostolate has a special field in areas where Catholics are few in number and widely dispersed. Here the laity who engage in the apostolate only as individuals, whether for the reasons already mentioned or for special reasons including those deriving also from their own professional activity, usefully gather into smaller groups for serious conversation without any more formal kind of establishment or organization, so that an indication of the community of the Church is always apparent to others as a true witness of love. In this way, by giving spiritual help to one another through friendship and the communicating of the benefit of their experience, they are trained to overcome the disadvantages of excessively isolated life and activity and to make their apostolate more productive.
Source: Apostolicam Actuositatem (Vatican.va)