Objection 1. It would seem that one ought to be withdrawn from entering religion through deference to one's parents. For it is not lawful to omit that which is of obligation in order to do that which is optional. Now deference to one's parents comes under an obligation of the precept concerning the honoring of our parents (Exodus 20:12); wherefore the Apostle says (1 Timothy 5:4): "If any widow have children or grandchildren, let her learn first to govern her own house, and to make a return of duty to her parents." But the entrance to religion is optional. Therefore it would seem that one ought not to omit deference to one's parents for the sake of entering religion.
Objection 2. Further, seemingly the subjection of a son to his father is greater than that of a slave to his master, since sonship is natural, while slavery results from the curse of sin, as appears from Genesis 9:25. Now a slave cannot set aside the service of his master in order to enter religion or take holy orders, as stated in the Decretals (Dist. LIV, cap. Si servus). Much less therefore can a son set aside the deference due to his father in order to enter religion.
Objection 3. Further, a man is more indebted to his parents than to those to whom he owes money. Now persons who owe money to anyone cannot enter religion. For Gregory says (Regist. viii, Ep. 5) that "those who are engaged in trade must by no means be admitted into a monastery, when they seek admittance, unless first of all they withdraw from public business" (Dist. liii, can. Legem.). Therefore seemingly much less may children enter religion in despite of their duty to their parents.
On the contrary, It is related (Matthew 4:22) that James and John "left their nets and father, and followed our Lord." By this, says Hilary (Can. iii in Matth.), "we learn that we who intend to follow Christ are not bound by the cares of the secular life, and by the ties of home."
I answer that, As stated above (101, 2, ad 2) when we were treating of piety, parents as such have the character of a principle, wherefore it is competent to them as such to have the care of their children. Hence it is unlawful for a person having children to enter religion so as altogether to set aside the care for their children, namely without providing for their education. For it is written (1 Timothy 5:8) that "if any man have not care of his own... he hath denied the faith, and is worse than an infidel."
Nevertheless it is accidentally competent to parents to be assisted by their children, in so far, to wit, as they are placed in a condition of necessity. Consequently we must say that when their parents are in such need that they cannot fittingly be supported otherwise than by the help of their children, these latter may not lawfully enter religion in despite of their duty to their parents. If, however, the parents' necessity be not such as to stand in great need of their children's assistance, the latter may, in despite of the duty they owe their parents, enter religion even against their parents' command, because after the age of puberty every freeman enjoys freedom in things concerning the ordering of his state of life, especially in such as belong to the service of God, and "we should more obey the Father of spirits that we may live ['Shall we not much more obey the Father of Spirits, and live?']," as says the Apostle (Hebrews 12:9), than obey our parents. Hence as we read (Matthew 8:22; Luke 9:62) our Lord rebuked the disciple who was unwilling to follow him forthwith on account of his father's burial: for there were others who could see to this, as Chrysostom remarks [Hom. xxvii in Matth.].
Reply to Objection 1. The commandment of honoring our parents extends not only to bodily but also to spiritual service, and to the paying of deference. Hence even those who are in religion can fulfil the commandment of honoring their parents, by praying for them and by revering and assisting them, as becomes religious, since even those who live in the world honor their parents in different ways as befits their condition.
Reply to Objection 2. Since slavery was imposed in punishment of sin, it follows that by slavery man forfeits something which otherwise he would be competent to have, namely the free disposal of his person, for "a slave belongs wholly to his master" [Aristotle, Polit. i, 2. On the other hand, the son, through being subject to his father, is not hindered from freely disposing of his person by transferring himself to the service of God; which is most conducive to man's good.
Reply to Objection 3. He who is under a certain fixed obligation cannot lawfully set it aside so long as he is able to fulfil it. Wherefore if a person is under an obligation to give an account to someone or to pay a certain fixed debt, he cannot lawfully evade this obligation in order to enter religion. If, however, he owes a sum of money, and has not wherewithal to pay the debt, he must do what he can, namely by surrendering his goods to his creditor. According to civil law [Cod. IV, x, de Oblig. et Action, 12 money lays an obligation not on the person of a freeman, but on his property, because the person of a freeman "is above all pecuniary consideration" [Dig. L, xvii, de div. reg. Jur. ant. 106,176]. Hence, after surrendering his property, he may lawfully enter religion, nor is he bound to remain in the world in order to earn the means of paying the debt.
On the other hand, he does not owe his father a special debt, except as may arise in a case of necessity, as stated above.
Source: Summa Theologica (New Advent)