Objection 1. It would seem that obedience does not belong to religious perfection. For those things seemingly belong to religious perfection, which are works of supererogation and are not binding upon all. But all are bound to obey their superiors, according to the saying of the Apostle (Hebrews 13:17), "Obey your prelates, and be subject to them." Therefore it would seem that obedience does not belong to religious perfection.
Objection 2. Further, obedience would seem to belong properly to those who have to be guided by the sense of others, and such persons are lacking in discernment. Now the Apostle says (Hebrews 5:1)4) that "strong meat is for the perfect, for them who by custom have their senses exercised to the discerning of good and evil." Therefore it would seem that obedience does not belong to the state of the perfect.
Objection 3. Further, if obedience were requisite for religious perfection, it would follow that it is befitting to all religious. But it is not becoming to all; since some religious lead a solitary life, and have no superior whom they obey. Again religious superiors apparently are not bound to obedience. Therefore obedience would seem not to pertain to religious perfection.
Objection 4. Further, if the vow of obedience were requisite for religion, it would follow that religious are bound to obey their superiors in all things, just as they are bound to abstain from all venery by their vow of continence. But they are not bound to obey them in all things, as stated above (Question 104, Article 5), when we were treating of the virtue of obedience. Therefore the vow of obedience is not requisite for religion.
Objection 5. Further, those services are most acceptable to God which are done freely and not of necessity, according to (2 Corinthians 9:7), "Not with sadness or of necessity." Now that which is done out of obedience is done of necessity of precept. Therefore those good works are more deserving of praise which are done of one's own accord. Therefore the vow of obedience is unbecoming to religion whereby men seek to attain to that which is better.
On the contrary, Religious perfection consists chiefly in the imitation of Christ, according to Matthew 19:21, "If thou wilt be perfect, go sell all [Vulgate: 'what'] thou hast, and give to the poor, and follow Me." Now in Christ obedience is commended above all according to (Philippians 2:8), "He became [Vulgate: 'becoming'] obedient unto death." Therefore seemingly obedience belongs to religious perfection.
I answer that, As stated above (A2,3) the religious state is a school and exercise for tending to perfection. Now those who are being instructed or exercised in order to attain a certain end must needs follow the direction of someone under whose control they are instructed or exercised so as to attain that end as disciples under a master. Hence religious need to be placed under the instruction and command of someone as regards things pertaining to the religious life; wherefore it is said (VII, qu. i, can. Hoc nequaquam): "The monastic life denotes subjection and discipleship." Now one man is subjected to another's command and instruction by obedience: and consequently obedience is requisite for religious perfection.
Reply to Objection 1. To obey one's superiors in matters that are essential to virtue is not a work of supererogation, but is common to all: whereas to obey in matters pertaining to the practice of perfection belongs properly to religious. This latter obedience is compared to the former as the universal to the particular. For those who live in the world, keep something for themselves, and offer something to God; and in the latter respect they are under obedience to their superiors: whereas those who live in religion give themselves wholly and their possessions to God, as stated above (1 and 3). Hence their obedience is universal.
Reply to Objection 2. As the Philosopher says (Ethic. ii, 1,2), by performing actions we contract certain habits, and when we have acquired the habit we are best able to perform the actions. Accordingly those who have not attained to perfection, acquire perfection by obeying, while those who have already acquired perfection are most ready to obey, not as though they need to be directed to the acquisition of perfection, but as maintaining themselves by this means in that which belongs to perfection.
Reply to Objection 3. The subjection of religious is chiefly in reference to bishops, who are compared to them as perfecters to perfected, as Dionysius states (Eccl. Hier. vi), where he also says that the "monastic order is subjected to the perfecting virtues of the bishops, and is taught by their godlike enlightenment." Hence neither hermits nor religious superiors are exempt from obedience to bishops; and if they be wholly or partly exempt from obedience to the bishop of the diocese, they are nevertheless bound to obey the Sovereign Pontiff, not only in matters affecting all in common, but also in those which pertain specially to religious discipline.
Reply to Objection 4. The vow of obedience taken by religious, extends to the disposition of a man's whole life, and in this way it has a certain universality, although it does not extend to all individual acts. For some of these do not belong to religion, through not being of those things that concern the love of God and of our neighbor, such as rubbing one's beard, lifting a stick from the ground and so forth, which do not come under a vow nor under obedience; and some are contrary to religion. Nor is there any comparison with continence whereby acts are excluded which are altogether contrary to religion.
Reply to Objection 5. The necessity of coercion makes an act involuntary and consequently deprives it of the character of praise or merit; whereas the necessity which is consequent upon obedience is a necessity not of coercion but of a free will, inasmuch as a man is willing to obey, although perhaps he would not be willing to do the thing commanded considered in itself. Wherefore since by the vow of obedience a man lays himself under the necessity of doing for God's sake certain things that are not pleasing in themselves, for this very reason that which he does is the more acceptable to God, though it be of less account, because man can give nothing greater to God, than by subjecting his will to another man's for God's sake. Hence in the Conferences of the Fathers (Coll. xviii, 7) it is stated that "the Sarabaitae are the worst class of monks, because through providing for their own needs without being subject to superiors, they are free to do as they will; and yet day and night they are more busily occupied in work than those who live in monasteries."
Source: Summa Theologica (New Advent)