3 And precisely to revive your confidence in Divine Aid, and to encourage you to continue in the practice of a fervent Christian life, We address this letter to you, and We avail ourselves of this occasion to remind you how, under the present difficult circumstances, the most efficacious means for a Christian restoration are - and also among you - above all the holiness of priests, and in the second place the correct formation of the laity in order that they may be capable of cooperating fruitfully in the Apostolate of the Hierarchy, so much more necessary in Mexico both because of the vastness of the territory and because of other circumstances known to all.
Source: Firmissimam Constantiam (Vatican.va)