Objection 1. It would seem that no religious order should be established for the works of the active life. For every religious order belongs to the state of perfection, as stated above (184, 5; 186, 1). Now the perfection of the religious state consists in the contemplation of divine things. For Dionysius says (Eccl. Hier. vi) that they are "called servants of God by reason of their rendering pure service and subjection to God, and on account of the indivisible and singular life which unites them by holy reflections," i.e. contemplations, "on invisible things, to the Godlike unity and the perfection beloved of God." Therefore seemingly no religious order should be established for the works of the active life.
Objection 2. Further, seemingly the same judgment applies to canons regular as to monks, according to Extra, De Postul., cap. Ex parte; and De Statu Monach., cap. Quod Dei timorem: for it is stated that "they are not considered to be separated from the fellowship of monks": and the same would seem to apply to all other religious. Now the monastic rule was established for the purpose of the contemplative life; wherefore Jerome says (Ep. lviii ad Paulin.): "If you wish to be what you are called, a monk," i.e. a solitary, "what business have you in a city?" The same is found stated in Extra, De Renuntiatione, cap. Nisi cum pridem; and De Regular., cap. Licet quibusdam. Therefore it would seem that every religious order is directed to the contemplative life, and none to the active life.
Objection 3. Further, the active life is concerned with the present world. Now all religious are said to renounce the world; wherefore Gregory says (Hom. xx in Ezech.): "He who renounces this world, and does all the good he can, is like one who has gone out of Egypt and offers sacrifice in the wilderness." Therefore it would seem that no religious order can be directed to the active life.
On the contrary, It is written (James 1:2)7): "Religion clean and undefiled before God and the Father, is this: to visit the fatherless and widows in their tribulation." Now this belongs to the active life. Therefore religious life can be fittingly directed to the active life.
I answer that, As stated above (Article 1), the religious state is directed to the perfection of charity, which extends to the love of God and of our neighbor. Now the contemplative life which seeks to devote itself to God alone belongs directly to the love of God, while the active life, which ministers to our neighbor's needs, belongs directly to the love of one's neighbor. And just as out of charity we love our neighbor for God's sake, so the services we render our neighbor redound to God, according to Matthew 25:40, "What you have done [Vulgate: 'As long as you did it'] to one of these My least brethren, you did it to Me." Consequently those services which we render our neighbor, in so far as we refer them to God, are described as sacrifices, according to (Hebrews 13:16), "Do not forget to do good and to impart, for by such sacrifices God's favor is obtained." And since it belongs properly to religion to offer sacrifice to God, as stated above (81, 1, ad 1; 4, ad 1), it follows that certain religious orders are fittingly directed to the works of the active life. Wherefore in the Conferences of the Fathers (Coll. xiv, 4) the Abbot Nesteros in distinguishing the various aims of religious orders says: "Some direct their intention exclusively to the hidden life of the desert and purity of heart; some are occupied with the instruction of the brethren and the care of the monasteries; while others delight in the service of the guesthouse," i.e. in hospitality.
Reply to Objection 1. Service and subjection rendered to God are not precluded by the works of the active life, whereby a man serves his neighbor for God's sake, as stated in the Article. Nor do these works preclude singularity of life; not that they involve man's living apart from his fellow-men, but in the sense that each man individually devotes himself to things pertaining to the service of God; and since religious occupy themselves with the works of the active life for God's sake, it follows that their action results from their contemplation of divine things. Hence they are not entirely deprived of the fruit of the contemplative life.
Reply to Objection 2. The same judgment applies to monks and to all other religious, as regards things common to all religious orders: for instance as regards their devoting themselves wholly to the divine service, their observance of the essential vows of religion, and their refraining from worldly business. But it does not follow that this likeness extends to other things that are proper to the monastic profession, and are directed especially to the contemplative life. Hence in the aforesaid Decretal, De Postulando, it is not simply stated that "the same judgment applies to canons regular" as "to monks," but that it applies "in matters already mentioned," namely that "they are not to act as advocates in lawsuits." Again the Decretal quoted, De Statu Monach., after the statement that "canons regular are not considered to be separated from the fellowship of monks," goes on to say: "Nevertheless they obey an easier rule." Hence it is evident that they are not bound to all that monks are bound.
Reply to Objection 3. A man may be in the world in two ways: in one way by his bodily presence, in another way by the bent of his mind. Hence our Lord said to His disciples (John 15:19): "I have chosen you out of the world," and yet speaking of them to His Father He said (John 17:11): "These are in the world, and I come to Thee." Although, then, religious who are occupied with the works of the active life are in the world as to the presence of the body, they are not in the world as regards their bent of mind, because they are occupied with external things, not as seeking anything of the world, but merely for the sake of serving God: for "they... use this world, as if they used it not," to quote (1 Corinthians 7:3)1. Hence (James 1:2)7) after it is stated that "religion clean and undefiled... is... to visit the fatherless and widows in their tribulation," it is added, "and to keep one's self unspotted from this world," namely to avoid being attached to worldly things.
Source: Summa Theologica (New Advent)