35. Let this be enough on this subject. Next in the order of belief comes, AND IN THE HOLY SPIRIT. The detailed, rather lengthy account of Christ recorded above has reference to the mystery of His incarnation and passion. Being taken in connection with His person, it has formed an interruption which has held up my discussion of the Holy Spirit. If our theme were exclusively the Godhead, we should say at the outset, I BELIEVE IN GOD THE FATHER ALMIGHTY, and then, IN JESUS CHRIST, HIS ONLY SON, OUR LORD: then in exactly the same way we should, without more ado, append, AND IN THE HOLY SPIRIT. All the intervening allusions to Christ, as I have pointed out, are concerned with His incarnate state. Consequently, we complete the mystery of the Trinity with our mention of the Holy Spirit. Just as we speak of the Father as one, there being no other Father, and of the only-begotten Son as one, there being no other only-begotten Son, so the Holy Spirit is also one, and there can be no other Holy Spirit. In order to bring out the distinction of Persons, you see, we employ separate terms expressive of relationship. Thus, He is to be taken as Father from whom are all things, and who Himself has no Father. The Third is the Holy Spirit, inasmuch as He proceeds from the mouth of God and sanctifies all things. At the same time, to emphasize the unity and identity of the Godhead in the Trinity, just as we say we believe IN GOD THE FATHER, prefixing the preposition IN, so we use the form IN CHRIST, HIS SON, and also IN THE HOLY SPIRIT. The meaning of what I have said will, however, be made plainer in the sequel.- Rufinus, A Commentary on the Apostles’ Creed, 35-39. (pp. 71-74 of J.N.D. Kelly's translation in Ancient Christian Writers, Volume 20)
36. Immediately after this clause follow the words, THE HOLY CHURCH, THE REMISSION OF SINS, THE RESURRECTION OF THE FLESH. The creed does not say: IN THE HOLY CHURCH, or IN THE REMISSION OF SINS, or IN THE RESURRECTION OF THE FLESH. Had the preposition been IN inserted, the force of these articles would have been identical with that of their predecessors. As it is, in the clauses in which our faith in the Godhead is laid down, we use the form, IN GOD THE FATHER, IN JESUS CHRIST HIS SON, and IN THE HOLY SPIRIT. In the other clauses, where the theme is not the Godhead but created beings and saving mysteries, the preposition IN is not interpolated. Hence we are not told to believe IN THE HOLY CHURCH, but that the Holy Church exists, speaking of it not as God, but as a Church gathered together for God. So Christians believe, not IN THE REMISSION OF SINS, but that there is a remission of sins, and not IN THE RESURRECTION OF THE FLESH, but that there is a resurrection of the flesh. Thus the effect of this monosyllabic preposition is to distinguish the Creator from His creatures, and to draw a boundary line between things divine and things human. It was this Holy Spirit, then, who inspired the Law and the Prophets in the Old Testament, and the Gospels and the Apostles in the New. So the Apostle remarks: All Scripture, inspired of God, is profitable to teach. Consequently, it seems appropriate at this point, basing myself on the records of the Fathers, to enumerate the books of the Old and New Testaments which, according to the tradition of our forefathers, are believed to have been inspired by the Holy Spirit Himself and to have been entrusted by Him to the churches of Christ.
37. In the Old Testament, then, first of all five books by Moses have been handed down―Genesis, Exodus, Leviticus, Numbers, and Deuteronomy; then Josue, the son of Nun, and Judges, together with Ruth; then four books of Kings, reckoned by the Jews as two, Paralipomenon [Chronicles], otherwise called the Book of Days; two books of Esdras, which the Jews count as one; and Esther. Of prophets we have Isaias, Jeremias, Ezechiel, Daniel, and, in addition, a single book of the Twelve Prophets. Job, also, and the Psalms of David are each of them one book. There are three which Solomon bequeathed to the churches, namely, Proverbs, Ecclesiastes, and the Canticle of Canticles. With these they completed the list of books belonging to the Old Testament. In the New there are four Gospels, those of Matthew, Mark, Luke, and John; the Acts of the Apostles, composed by Luke; fourteen Epistles by the Apostle Paul; two by the Apostle Peter; one by James, brother of the Lord and Apostle; one by Jude; three by John; and the Apocalypse of John.
38. These are the writings which the Fathers included in the canon, and on which they desired the affirmations of our faith to be based. At the same time we should appreciate that there are certain other books which our predecessors designated ‘ecclesiastical’ rather than ‘canonical.’ Thus, there is the Wisdom of Solomon, as we call it; and another Wisdom, ascribed to the son of Sirach. This latter is known by the general title Ecclesiasticus among Latin-speaking people, the description pointing, not to the author of the book, but to the character of the writing. The Book of Tobias belongs to the same class, as do Judith and the books of the Machabees. In the New Testament we have the little work known as The Book of the Shepherd, or Hermas, and the book which is named The Two Ways, and The Judgment of Peter. They desired that all these should be read in the churches, but that appeal should not be made to them on points of faith. The other writings they designated ‘apocryphal,’ refusing to allow them to be read out in church. Such, the, is the traditional canon handed down to us by the Fathers. As I remarked above, I have thought this the proper place to draw attention to it for the information of catechumens receiving their first lessons in the Church and its faith, so that they may be in no doubt about the wellsprings from which their draughts of the word of God must be taken.
39. The next clause in the ordered statement of our faith runs, THE HOLY CHURCH. I have already explained in what precedes why they did not say IN THE HOLY CHURCH at this point too. So the faithful, having had the belief in one God mysteriously triune inculcated in the foregoing sections, are now in addition required to believe in the existence of one holy Church, a Church, that is, in which there is one faith and one baptism, and in which we believe in one God the Father, one Lord Jesus Christ His Son, and one Holy Spirit.
(Thanks to David King for his assistance in identifying and transcribing this quotation.)