Thomas Aquinas

“ If an advocate believes from the outset that the cause is just, and discovers afterwards while the case is proceeding that it is unjust, he ought not to throw up his brief in such a way as to help the other side, or so as to reveal the secrets of his client to the other party. ”

“ Now to be busy with Divine things and to be busy about sin are contrary to one another. Therefore it is unfitting that some should be debarred from the office of advocate, on account of religion, as monks and clerics, while others are debarred on account of sin, as persons of ill-repute and heretics.
Objection 3: Further, a man should love his neighbor as himself. Now it is a duty of love for an advocate to plead a person's cause. Therefore it is unfitting that certain persons should be debarred from pleading the cause of others, while they are allowed to advocate their own cause. ”

“ Man is not bound to do gratuitously whatever he can do from motives of mercy: else no man could lawfully sell anything, since anything may be given from motives of mercy. But when a man does give a thing out of mercy, he should seek, not a human, but a Divine reward. In like manner an advocate, when he mercifully pleads the cause of a poor man, should have in view not a human but a Divine meed ”

“ Though knowledge of law is something spiritual, the use of that knowledge is accomplished by the work of the body: hence it is lawful to take money in payment of that use, else no craftsman would be allowed to make profit by his art. ”

“ Secondly, on account of some personal defect, either of body (for instance a blind man whose attendance in a court of justice would be unbecoming) or of soul, for it ill becomes one who has disdained to be just himself, to plead for the justice of another. Wherefore it is unbecoming that persons of ill repute, unbelievers, and those who have been convicted of grievous crimes should be advocates. ”

“ It may happen however that these circumstances concur, and then we have to consider whether this particular man stands in such a need that it is not easy to see how he can be succored otherwise, and then one is bound to bestow the work of mercy on him. ”

“ Lastly he says, "or any other circumstance," because one ought to show kindness to those especially who are by any tie whatever united to us, according to 1 Tim. 5:8, "If any man have not care of his own, and especially of those of his house, he hath denied the faith and is worse than an infidel." ”