Objection 1. It would seem that it is unsuitable for the articles of faith to be embodied in a symbol. Because Holy Writ is the rule of faith, to which no addition or subtraction can lawfully be made, since it is written (Deuteronomy 4:2): "You shall not add to the word that I speak to you, neither shall you take away from it." Therefore it was unlawful to make a symbol as a rule of faith, after the Holy Writ had once been published.
Objection 2. Further, according to the Apostle (Ephesians 4:5) there is but "one faith." Now the symbol is a profession of faith. Therefore it is not fitting that there should be more than one symbol.
Objection 3. Further, the confession of faith, which is contained in the symbol, concerns all the faithful. Now the faithful are not all competent to believe in God, but only those who have living faith. Therefore it is unfitting for the symbol of faith to be expressed in the words: "I believe in one God."
Objection 4. Further, the descent into hell is one of the articles of faith, as stated above (Article 8). But the descent into hell is not mentioned in the symbol of the Fathers. Therefore the latter is expressed inadequately.
Objection 5. Further, Augustine (Tract. xxix in Joan.) expounding the passage, "You believe in God, believe also in Me" (John 14:1) says: "We believe Peter or Paul, but we speak only of believing 'in' God." Since then the Catholic Church is merely a created being, it seems unfitting to say: "In the One, Holy, Catholic and Apostolic Church."
Objection 6. Further, a symbol is drawn up that it may be a rule of faith. Now a rule of faith ought to be proposed to all, and that publicly. Therefore every symbol, besides the symbol of the Fathers, should be sung at Mass. Therefore it seems unfitting to publish the articles of faith in a symbol.
On the contrary, The universal Church cannot err, since she is governed by the Holy Ghost, Who is the Spirit of truth: for such was Our Lord's promise to His disciples (John 16:13): "When He, the Spirit of truth, is come, He will teach you all truth." Now the symbol is published by the authority of the universal Church. Therefore it contains nothing defective.
I answer that, As the Apostle says (Hebrews 11:6), "he that cometh to God, must believe that He is." Now a man cannot believe, unless the truth be proposed to him that he may believe it. Hence the need for the truth of faith to be collected together, so that it might the more easily be proposed to all, lest anyone might stray from the truth through ignorance of the faith. It is from its being a collection of maxims of faith that the symbol [The Greek symballein] takes its name.
Reply to Objection 1. The truth of faith is contained in Holy Writ, diffusely, under various modes of expression, and sometimes obscurely, so that, in order to gather the truth of faith from Holy Writ, one needs long study and practice, which are unattainable by all those who require to know the truth of faith, many of whom have no time for study, being busy with other affairs. And so it was necessary to gather together a clear summary from the sayings of Holy Writ, to be proposed to the belief of all. This indeed was no addition to Holy Writ, but something taken from it.
Reply to Objection 2. The same doctrine of faith is taught in all the symbols. Nevertheless, the people need more careful instruction about the truth of faith, when errors arise, lest the faith of simple-minded persons be corrupted by heretics. It was this that gave rise to the necessity of formulating several symbols, which nowise differ from one another, save that on account of the obstinacy of heretics, one contains more explicitly what another contains implicitly.
Reply to Objection 3. The confession of faith is drawn up in a symbol in the person, as it were, of the whole Church, which is united together by faith. Now the faith of the Church is living faith; since such is the faith to be found in all those who are of the Church not only outwardly but also by merit. Hence the confession of faith is expressed in a symbol, in a manner that is in keeping with living faith, so that even if some of the faithful lack living faith, they should endeavor to acquire it.
Reply to Objection 4. No error about the descent into hell had arisen among heretics, so that there was no need to be more explicit on that point. For this reason it is not repeated in the symbol of the Fathers, but is supposed as already settled in the symbol of the Apostles. For a subsequent symbol does not cancel a preceding one; rather does it expound it, as stated above (ad 2).
Reply to Objection 5. If we say: "'In' the holy Catholic Church," this must be taken as verified in so far as our faith is directed to the Holy Ghost, Who sanctifies the Church; so that the sense is: "I believe in the Holy Ghost sanctifying the Church." But it is better and more in keeping with the common use, to omit the 'in,' and say simply, "the holy Catholic Church," as Pope Leo [Rufinus, Comm. in Sym. Apost.] observes.
Reply to Objection 6. Since the symbol of the Fathers is an explanation of the symbol of the Apostles, and was drawn up after the faith was already spread abroad, and when the Church was already at peace, it is sung publicly in the Mass. On the other hand the symbol of the Apostles, which was drawn up at the time of persecution, before the faith was made public, is said secretly at Prime and Compline, as though it were against the darkness of past and future errors.
Source: Summa Theologica (New Advent)