Objection 1. It would seem that one ought not to be bound by vow to enter religion. For in making his profession a man is bound by the religious vow. Now before profession a year of probation is allowed, according to the rule of the Blessed Benedict (lviii) and according to the decree of Innocent IV [Sext. Decret., cap. Non solum., de Regular. et Transeunt, ad Relig.] who moreover forbade anyone to be bound to the religious life by profession before completing the year of probation. Therefore it would seem that much less ought anyone while yet in the world to be bound by vow to enter religion.
Objection 2. Further, Gregory says (Regist. xi, Ep. 15): Jews "should be persuaded to be converted, not by compulsion but of their own free will" (Dist. xlv, can. De Judaeis). Now one is compelled to fulfil what one has vowed. Therefore no one should be bound by vow to enter religion.
Objection 3. Further, no one should give another an occasion of falling; wherefore it is written (Exodus 21:33-34): "If a man open a pit... and an ox or an ass fall into it, the owner of the pit shall pay the price of the beasts." Now through being bound by vow to enter religion it often happens that people fall into despair and various sins. Therefore it would seem that one ought not to be bound by vow to enter religion.
On the contrary, It is written, (Psalm 75:12): "Vow ye, and pay to the Lord your God"; and a gloss of Augustine says that "some vows concern the individual, such as vows of chastity, virginity, and the like." Consequently Holy Scripture invites us to vow these things. But Holy Scripture invites us only to that which is better. Therefore it is better to bind oneself by vow to enter religion.
I answer that, As stated above (Question 88, Article 6), when we were treating of vows, one and the same work done in fulfilment of a vow is more praiseworthy than if it be done apart from a vow, both because to vow is an act of religion, which has a certain pre-eminence among the virtues, and because a vow strengthens a man's will to do good; and just as a sin is more grievous through proceeding from a will obstinate in evil, so a good work is the more praiseworthy through proceeding from a will confirmed in good by means of a vow. Therefore it is in itself praiseworthy to bind oneself by vow to enter religion.
Reply to Objection 1. The religious vow is twofold. One is the solemn vow which makes a man a monk or a brother in some other religious order. This is called the profession, and such a vow should be preceded by a year's probation, as the objection proves. The other is the simple vow which does not make a man a monk or a religious, but only binds him to enter religion, and such a vow need not be preceded by a year's probation.
Reply to Objection 2. The words quoted from Gregory must be understood as referring to absolute violence. But the compulsion arising from the obligation of a vow is not absolute necessity, but a necessity of end, because after such a vow one cannot attain to the end of salvation unless one fulfil that vow. Such a necessity is not to be avoided; indeed, as Augustine says (Ep. cxxvii ad Armentar. et Paulin.), "happy is the necessity that compels us to better things."
Reply to Objection 3. The vow to enter religion is a strengthening of the will for better things, and consequently, considered in itself, instead of giving a man an occasion of falling, withdraws him from it. But if one who breaks a vow falls more grievously, this does not derogate from the goodness of the vow, as neither does it derogate from the goodness of Baptism that some sin more grievously after being baptized.
Source: Summa Theologica (New Advent)