13 Now in order that the joyful fruits we have mentioned may flow forth from these sacred Exercises, these must needs be made with due care and diligence. For if the exercises are performed merely for the sake of custom, or tardily, and with hesitation, little or no advantage will be derived from them; wherefore before all things it is necessary that the mind, assisted by solitude should devote itself to the sacred meditations, leaving aside all the cares and solicitudes of daily life. For as that golden book, the Imitation of Christ , clearly teaches: " The devout soul makes progress in silence and in peace." For this reason, although we regard those meditations as worthy of praise and pastoral approval in which many make the exercises together in public - for these have received many blessings from God - still we most strongly recommend those Spiritual Exercises which are made in private, and are called "closed." For in these a man is more easily separated from intercourse with creatures and concentrates the dissipated powers of his soul on God himself and on the contemplation of eternal truths.
Source: Mens Nostra (Vatican.va)