Le Pelerinage de Lourdes §41

⁴¹ But in itself this experience of a few brief days of pilgrimage is not usually sufficient to engrave in indelible letters the call of Mary to a genuine spiritual conversion. That is why We exhort the shepherds of dioceses and all priests to outdo one another in zeal that the centenary pilgrimages may benefit by preparation, and, above all, by a follow-up which will be as conducive as possible to a profound and lasting action of grace.