Objection 1. It would seem that respect of persons does not take place in the dispensation of spiritual goods. For it would seem to savor of respect of persons if a man confers ecclesiastical dignity or benefice on account of consanguinity, since consanguinity is not a cause whereby a man is rendered worthy of an ecclesiastical benefice. Yet this apparently is not a sin, for ecclesiastical prelates are wont to do so. Therefore the sin of respect of persons does not take place in the conferring of spiritual goods.
Objection 2. Further, to give preference to a rich man rather than to a poor man seems to pertain to respect of persons, according to James 2:2-3. Nevertheless dispensations to marry within forbidden degrees are more readily granted to the rich and powerful than to others. Therefore the sin of respect of persons seems not to take place in the dispensation of spiritual goods.
Objection 3. Further, according to jurists [Cap. Cum dilectus.] it suffices to choose a good man, and it is not requisite that one choose the better man. But it would seem to savor of respect of persons to choose one who is less good for a higher position. Therefore respect of persons is not a sin in spiritual matters.
Objection 4. Further, according to the law of the Church (Cap. Cum dilectus.) the person to be chosen should be "a member of the flock." Now this would seem to imply respect of persons, since sometimes more competent persons would be found elsewhere. Therefore respect of persons is not a sin in spiritual matters.
On the contrary, It is written (James 2:1): "Have not the faith of our Lord Jesus Christ... with respect of persons." On these words a gloss of Augustine says: "Who is there that would tolerate the promotion of a rich man to a position of honor in the Church, to the exclusion of a poor man more learned and holier?" [Augustine, Ep. ad Hieron. clxvii.]
I answer that, As stated above (Article 1), respect of persons is a sin, in so far as it is contrary to justice. Now the graver the matter in which justice is transgressed, the more grievous the sin: so that, spiritual things being of greater import than temporal, respect of persons is a more grievous sin in dispensing spiritualities than in dispensing temporalities. And since it is respect of persons when something is allotted to a person out of proportion to his deserts, it must be observed that a person's worthiness may be considered in two ways. First, simply and absolutely: and in this way the man who abounds the more in the spiritual gifts of grace is the more worthy. Secondly, in relation to the common good; for it happens at times that the less holy and less learned man may conduce more to the common good, on account of worldly authority or activity, or something of the kind. And since the dispensation of spiritualities is directed chiefly to the common good, according to 1 Corinthians 12:7, "The manifestation of the Spirit is given to every man unto profit," it follows that in the dispensation of spiritualities the simply less good are sometimes preferred to the better, without respect of persons, just as God sometimes bestows gratuitous graces on the less worthy.
Reply to Objection 1. We must make a distinction with regard to a prelate's kinsfolk: for sometimes they are less worthy, both absolutely speaking, and in relation to the common good: and then if they are preferred to the more worthy, there is a sin of respect of persons in the dispensation of spiritual goods, whereof the ecclesiastical superior is not the owner, with power to give them away as he will, but the dispenser, according to 1 Corinthians 4:1, "Let a man so account of us as of the ministers of Christ, and the dispensers of the mysteries of God." Sometimes however the prelate's kinsfolk are as worthy as others, and then without respect of persons he can lawfully give preference to his kindred since there is at least this advantage, that he can trust the more in their being of one mind with him in conducting the business of the Church. Yet he would have to forego so doing for fear of scandal, if anyone might take an example from him and give the goods of the Church to their kindred without regard to their deserts.
Reply to Objection 2. Dispensations for contracting marriage came into use for the purpose of strengthening treaties of peace: and this is more necessary for the common good in relation to persons of standing, so that there is no respect of persons in granting dispensations more readily to such persons.
Reply to Objection 3. In order that an election be not rebutted in a court of law, it suffices to elect a good man, nor is it necessary to elect the better man, because otherwise every election might have a flaw. But as regards the conscience of an elector, it is necessary to elect one who is better, either absolutely speaking, or in relation to the common good. For if it is possible to have one who is more competent for a post, and yet another be preferred, it is necessary to have some cause for this. If this cause have anything to do with the matter in point, he who is elected will, in this respect, be more competent; and if that which is taken for cause have nothing to do with the matter, it will clearly be respect of persons.
Reply to Objection 4. The man who is taken from among the members of a particular Church, is generally speaking more useful as regards the common good, since he loves more the Church wherein he was brought up. For this reason it was commanded (Deuteronomy 17:15): "Thou mayest not make a man of another nation king, who is not thy brother."
Source: Summa Theologica (New Advent)