From Pope Pius XI’s letter Umbratilem, approving the statutes of the Carthusian Order. The Carthusians are similar to Trappists in many ways… they are revered for their great devotion to solitude and simplicity.

All those, who, according to their rule, lead a life of solitude remote from the din and follies of the world, and who not only assiduously contemplate the divine mysteries and the eternal truths, and pour forth ardent and continual prayers to God that his kingdom may flourish and be daily spread more widely, but who also atone for the sins of others still more than for their own mortification, prescribed or voluntary, of mind and body – such indeed must be said to have chosen the better part, like Mary of Bethany.

… Since the whole object of this institution lay in this, that the monks, each one in the privacy of his cell, unoccupied with any exterior ministry and having nothing to do with it, should fix their thoughts exclusively on things of heaven, wonderful was the benefit that accrued from it to Christian society.

… Consequently it was highly important for the Church that this most holy form of life, which had been kept unimpaired for so many centuries in monasteries, should be restored to its pristine vigour, so that there should never be lacking men and women of prayer who, unimpeded by any other care, would be perpetually besieging the Divine Mercy and would thus draw down from heaven benefits of every sort upon people, too neglectful of their salvation.