Where is that taught? Evidence? If it was explicitly believed at the time the Creed was written…then why didn’t they write it that way?
I only have a moment to reply. Regarding evidence the filioque was believed at the time of the Creed. As you mentioned, the doctrines of the Holy Ghost were added at the Council of Constantinople, which I think took place in the year 381. Here’s some other quotes from the same time period:
Hilary of Poitiers, AD357: “Concerning the Holy Spirit . . . it is not necessary to speak of him who must be acknowledged,
who is from the Father and the Son, his sources” (The Trinity 2:29).
The Athanasian Creed, AD400: “[W]e venerate one God in the Trinity, and the Trinity in oneness. . . . The Father was not made nor created nor begotten by anyone. The Son is from the Father alone, not made nor created, but begotten. The Holy Spirit is from the Father
and the Son [filioque], not made nor created nor begotten, but proceeding” (Athanasian Creed).
Epiphanius of Salamis, AD374: “The Father always existed and the Son always existed, and the Spirit breathes from the Father
and the Son” (The Man Well-Anchored 75).
Ambrose of Milan, 381: "Just as the Father is the fount of life, so too, there are many who have stated that the Son is designated as the fount of life. It is said, for example that with you, Almighty God, your Son is the fount of life, that is, the fount of the Holy Spirit. For the Spirit is life, just as the Lord says: ‘The words which I have spoken to you are Spirit and life’. … “The Holy Spirit, when he proceeds from the Father
and the Son, does not separate himself from the Father and does not separate himself from the Son” (The Holy Spirit ).
The following quote from St. Augustine is virtually identical to what the Council of Florence taught.
Augustine, 408: “If that which is given has for its principle the one by whom it is given, because it did not receive from anywhere else that which proceeds from the giver, then it must be confessed that
the Father and the Son are the principle of the Holy Spirit, not two principles, but just as the Father and the Son are one God . . . relative to the Holy Spirit, they are one principle” (The Trinity 5:14:15 [A.D. 408]).
I could provide more quotes, but these suffice to show that the filioque was believed by the Fathers of the East and West at the time of the Council of Constantinople.
As I mentioned in an earlier post, the reason the filioque was not included is because it was not being called in question at the time. What was denied was that the Holy Ghost proceeded
from the Father. That is why the Creed explicitly affirmed what it did. When a later heresy questioned the procession of the Holy Ghost from the Son, the filioque was added.
You need to read writings from Catholics regarding the filioque, not those put out by the Orthodox - a sect that denies the Primacy of the Pope and 13 general councils.
LoyalViews: Regarding your question. My point was that the Catholic Church is the true Church, and the Orthodox - who reject the office of “the rock upon whom the Church was built” - as well as 13 general councils, are not a the Church. They used to be part of the true Church, but not anymore.