This formula was looked upon as the bulwark of orthodoxy, and was introduced into the Creed, to which was added, in consequence, the word Filioque (and from the Son) after the words proceeding from the Father.
That addition, made by a local church which had no pretensions to infallibility, was for this very cause irregular. It was further wrong in giving a conception of the Trinity contrary to the teaching of the Scriptures, according to which there is in God but one principle, which is the Father, from which proceed, from all eternity, the Word by generation, and the Spirit by procession. As the quality of a principle forms the distinctive character of the Father's personality, it evidently cannot be attributed to the Word without ascribing to Him that which is the distinctive attribute of another Divine Person. Thus the French and Spanish bishops, wishing to defend in the Trinity the unity of essence or of substance, attacked the personal distinction and confounded the attributes which are the very basis of that distinction.
Another serious errour on their part was in giving a decision without first ascertaining that the words which they employed were authorized by Catholic tradition. Outside of the perpetual and established doctrine, no bishop can teach any thing without danger of falling into the most serious errours.
The dogmatic truths of Christianity relating to the very essence of God — that is, of the Infinite — are necessarily mysterious; hence no one should presume to teach them of his own authority. Even the Church herself only preserves them as she has received them. Revelation is a deposit confided by God to His Church, and not a philosophical synthesis which may be modified. Without doubt these Spanish and French bishops had no other end in view but in the clearest manner to expound the dogma of the Trinity; but their exposition, not having the traditional character, was an errour.
