Consider how different the world would have to be, in order for a husband and wife to simultaneously give birth to a single child. We can't really picture what it would look like, or how it would even be possible. For such a thing to happen, it would not require some small, insignificant modification — it would require a radically different universe, one which we cannot even imagine — That’s not a minor change.
In the same way, it is a different faith — it is a different doctrine of the Trinity — whenever you say that the Holy Spirit proceeds from both the Father and the Son.
There is a major difference in the way that Roman Catholics understand the doctrine of the Trinity, and the way the Orthodox Church has always taught the doctrine of the Trinity.
In John chapter fifteen, Jesus mentions the Holy Spirit “who proceeds from the Father” (John 15:26). And He stops there. Jesus did not say He proceeds from the Father “and from Me.”

Who was begotten by the Father? — The Son.
Who proceeds from the Father? — The Holy Spirit.
This idea of "proceeding" is different from being “begotten” or “giving birth”, but there are enough similarities that we can make a helpful comparison.
Would it make any sense, if I said that my mother and my father simultaneously gave birth to me? Of course not. They are both my parents, but only one of them gave birth to me. It is not possible for two people to give birth to the same baby. I cannot even picture that, and I don’t want to.
Similarly, it makes no sense whatsoever to say that the Holy Spirit proceeds from the Father and the Son. That’s just as nonsensical as saying that your mother and father both gave birth to you.
The Holy Spirit did not proceed from the Father and the Son.
In John fifteen, Jesus says that the Spirit proceeds from the Father. Period.
He didn’t say anything else.
A few hundred years ago, the Roman Catholic church changed that. And in the Nicene Creed, they started adding things. Instead of being faithful to what is written in Scripture, they changed it and said the Holy Spirit proceeds from the Father and the Son. In Latin, it is just one word – filioque – and in English it is translated “and the Son.”
Consider how different the world would have to be, in order for a husband and wife to simultaneously give birth to a single child. We can't really picture what it would look like, or how it would even be possible. For such a thing to happen, it would not require some small, insignificant modification — it would require a radically different universe, one which we cannot even imagine — That’s not a minor change.
In the same way, it is a different faith — it is a different doctrine of the Trinity — whenever you say that the Holy Spirit proceeds from both the Father and the Son.
It seems like such a simple change. It’s just one little word, just one little phrase. But it has major implications. It is a radical change. It introduces changes within the Godhead, mirroring the errors of multiple heresies which attacked the Early Church. As one priest has explained in the article, Why the Filioque is a Heresy, this single change to the doctrine of the Trinity requires us to embrace the heresies of Sabellianism, Eunomianism, or Pneumatomachianism, either distorting our understanding of the Father, or else thinking that the Holy Spirit is a created being — a mere creature.
And as multiple theologians and church historians have illustrated in various writings, that one change – on a foundational level – bears bad fruit that ultimately changes other doctrines and beliefs. Some of the errors in Roman Catholic teachings today, can be traced back to their misunderstanding of the doctrine of the Trinity.
Around 800 years ago — back in the 1200s — the Roman Catholics dogmatized this change, saying that we are required to believe that the Spirit proceeds from both the Father and the Son. They dogmatized this error at the Second Council of Lyons.
Three hundred years later — in the 1500s — numerous Protestants broke away from Rome. They rejected some of Rome's teachings, but not all. Protestants retained the Roman Catholic changes to the doctrine of the Trinity, and thus many Protestants continue paying homage to Roman Catholicism even today. Among those Protestants who kept the Nicene Creed, they kept Rome's modified version of it, asserting that the Spirit proceeds from both the Father and the Son.
Meanwhile, the Orthodox Church has kept the Creed unchanged. The Nicene Creed was first written in the fourth century, and in sixteen hundred years we have not changed it.
In John fifteen, Jesus said that the Spirit proceeds from the Father. Likewise, in the Orthodox Church — in our Nicene Creed – we agree that the Spirit proceeds from the Father. Period.
As Orthodox Christians, we do not change the doctrine of the Holy Trinity.
And just as we refuse to change the doctrine of the Trinity, we refuse to change any other doctrine. For two thousand years, we have kept the Faith unchanged. We do not change with the times, with the culture, or according to peoples' preferences.
The reason we don’t change these things is because, as the Bride of Christ, we are not focused on ourselves and our own personal desires. Rather, in humility, we focus on Christ. We are dedicated to Him, to who He is, to what He likes, and to what He has revealed.

