The interest of this creed is as much in its silences as in its clauses. It does not say that the Son is of one being with the Father, because the question that word answered had not yet been asked in that form. It does not describe the Holy Spirit beyond naming him. It does not define the church, the forgiveness of sins or the resurrection, all of which it lists and none of which it explains. It anathematises nobody.
Later creeds fill exactly these gaps, and the reason is always the same: a dispute arose, a party read the old words in a way the majority would not accept, and new words were added to close the reading off. The Nicene homoousios, the Chalcedonian adverbs and the Athanasian clauses are all repairs to a fence that this creed did not need. Reading them beside the Old Roman Symbol shows what each controversy actually cost in words.
The symbol itself passed out of use as a text and survived as a parent. The Apostles Creed is its direct descendant, reworked into declaratory form and fixed in Gaul, and the baptismal creeds of the other Western churches are its cousins. When a congregation today says I believe in God the Father almighty, they are answering a question that has been left out of the sentence.