40 When they see the devotion of the stretcher-bearers and the serene peace of the invalids, when they consider the spirit of brotherhood which unites the faithful of all races in a single prayer, when they observe the spontaneous mutual assistance and the sincere fervor of the pilgrims kneeling before the grotto, then the best of men are seized by the appeal of a life more completely dedicated to the service of God and their brothers; the less fervent become conscious of their lukewarmness and return to the road of prayer; quite hardened and skeptical sinners are often touched by grace, or at least, if they are honest, are moved by the testimony of this "multitude of believers of one heart and one soul."
Source: Le Pelerinage de Lourdes (Vatican.va)