Objection 1. It would seem unlawful for religious to beg. For Augustine says (De oper. Monach. xxviii): "The most cunning foe has scattered on all sides a great number of hypocrites wearing the monastic habit, who go wandering about the country," and afterwards he adds: "They all ask, they all demand to be supported in their profitable penury, or to be paid for a pretended holiness." Therefore it would seem that the life of mendicant religious is to be condemned.
Objection 2. Further, it is written (1 Thessalonians 4:11): "That you... work with your own hands as we commanded you, and that you walk honestly towards them that are without: and that you want nothing of any man's": and a gloss on this passage says: "You must work and not be idle, because work is both honorable and a light to the unbeliever: and you must not covet that which belongs to another and much less beg or take anything." Again a gloss [St. Augustine, (De oper. Monach. iii)] on (2 Thessalonians 3:10), "If any man will not work," etc. says: "He wishes the servants of God to work with the body, so as to gain a livelihood, and not be compelled by want to ask for necessaries." Now this is to beg. Therefore it would seem unlawful to beg while omitting to work with one's hands.
Objection 3. Further, that which is forbidden by law and contrary to justice, is unbecoming to religious. Now begging is forbidden in the divine law; for it is written (Deuteronomy 15:4): "There shall be no poor nor beggar among you," and (Psalm 36:25): "I have not seen the just forsaken, nor his seed seeking bread." Moreover an able-bodied mendicant is punished by civil law, according to the law (XI, xxvi, de Valid. Mendicant.). Therefore it is unfitting for religious to beg.
Objection 4. Further, "Shame is about that which is disgraceful," as Damascene says (De Fide Orth. ii, 15). Now Ambrose says (De Offic. i, 30) that "to be ashamed to beg is a sign of good birth." Therefore it is disgraceful to beg: and consequently this is unbecoming to religious.
Objection 5. Further, according to our Lord's command it is especially becoming to preachers of the Gospel to live on alms, as stated above (Article 4). Yet it is not becoming that they should beg, since a gloss on 2 Timothy 2:6, "The husbandman, that laboreth," etc. says: "The Apostle wishes the gospeler to understand that to accept necessaries from those among whom he labors is not mendicancy but a right." Therefore it would seem unbecoming for religious to beg.
On the contrary, It becomes religious to live in imitation of Christ. Now Christ was a mendicant, according to Psalm 39:18, "But I am a beggar and poor"; where a gloss says: "Christ said this of Himself as bearing the 'form of a servant,'" and further on: "A beggar is one who entreats another, and a poor man is one who has not enough for himself." Again it is written (Psalm 69:6): "I am needy and poor"; where a gloss says: "'Needy,' that is a suppliant; 'and poor,' that is, not having enough for myself, because I have no worldly wealth." And Jerome says in a letter [Reference unknown]: "Beware lest whereas thy Lord," i.e. Christ, "begged, thou amass other people's wealth." Therefore it becomes religious to beg.
I answer that, Two things may be considered in reference to mendicancy. The first is on the part of the act itself of begging, which has a certain abasement attaching to it; since of all men those would seem most abased who are not only poor, but are so needy that they have to receive their meat from others. On this way some deserve praise for begging out of humility, just as they abase themselves in other ways, as being the most efficacious remedy against pride which they desire to quench either in themselves or in others by their example. For just as a disease that arises from excessive heat is most efficaciously healed by things that excel in cold, so proneness to pride is most efficaciously healed by those things which savor most of abasement. Hence it is said in the Decretals (II, cap. Si quis semel, de Paenitentia): "To condescend to the humblest duties, and to devote oneself to the lowliest service is an exercise of humility; for thus one is able to heal the disease of pride and human glory." Hence Jerome praises Fabiola (Ep. lxxvii ad ocean.) for that she desired "to receive alms, having poured forth all her wealth for Christ's sake." The Blessed Alexis acted in like manner, for, having renounced all his possessions for Christ's sake he rejoiced in receiving alms even from his own servants. It is also related of the Blessed Arsenius in the Lives of the Fathers (v, 6) that he gave thanks because he was forced by necessity to ask for alms. Hence it is enjoined to some people as a penance for grievous sins to go on a pilgrimage begging. Since, however, humility like the other virtues should not be without discretion, it behooves one to be discreet in becoming a mendicant for the purpose of humiliation, lest a man thereby incur the mark of covetousness or of anything else unbecoming. Secondly, mendicancy may be considered on the part of that which one gets by begging: and thus a man may be led to beg by a twofold motive. First, by the desire to have wealth or meat without working for it, and such like mendicancy is unlawful; secondly, by a motive of necessity or usefulness. The motive is one of necessity if a man has no other means of livelihood save begging; and it is a motive of usefulness if he wishes to accomplish something useful, and is unable to do so without the alms of the faithful. Thus alms are besought for the building of a bridge, or church, or for any other work whatever that is conducive to the common good: thus scholars may seek alms that they may devote themselves to the study of wisdom. On this way mendicancy is lawful to religious no less than to seculars.
Reply to Objection 1. Augustine is speaking there explicitly of those who beg from motives of covetousness.
Reply to Objection 2. The first gloss speaks of begging from motives of covetousness, as appears from the words of the Apostle; while the second gloss speaks of those who without effecting any useful purpose, beg their livelihood in order to live in idleness. on the other hand, he lives not idly who in any way lives usefully.
Reply to Objection 3. This precept of the divine law does not forbid anyone to beg, but it forbids the rich to be so stingy that some are compelled by necessity to beg. The civil law imposes a penalty on able-bodied mendicants who beg from motives neither of utility nor of necessity.
Reply to Objection 4. Disgrace is twofold; one arises from lack of honesty [Cf. 145, 1], the other from an external defect, thus it is disgraceful for a man to be sick or poor. Such like uncomeliness of mendicancy does not pertain to sin, but it may pertain to humility, as stated above.
Reply to Objection 5. Preachers have the right to be fed by those to whom they preach: yet if they wish to seek this by begging so as to receive it as a free gift and not as a right this will be a mark of greater humility.
Source: Summa Theologica (New Advent)