A regular reader of Abyssum sends this question:
The Creed that we pray after the homily says in part “I believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father and the Son …”.Part of the discussion at our ritual of post Mass breakfast at Denny’s was what does “who proceeds from the Father and the Son” mean? There was no consensus at breakfast other than “John, why don’t you ask Bishop Gracida”.
The question has been around for a long time because it pertains to our understanding a reality for which there is nothing in nature that can be referred to in describing it using human language. The reality is the existence in God of three Persons, called by Jesus Christ: “Father”, “Son” and “Holy Spirit”. Jesus Christ revealed to us their existence, but he did not tell us much about their relationship, especially how the relationship came to be.
That relationship puzzled men for the first four centuries of the Christian Era, I am confident, but it did not become a problem for the Church until the heretic, Arias, began preaching that Jesus Christ was a man but not God. The Arian Controversy was settled by the bishops of the Council of Nicea.
The Fathers of the Council struggled with how to ‘explain in, the Creed they promulgated about the God, after saying “I believe in One God…”, a profession of belief in the existence of two additional persons in God. I am confident that they searched all the words in the Greek language for a word and finally the settled on the word paradises which is translated in English as procession.
In A Modern Catholic Dictionary Father John Hardon, S.J. (yes Elizabeth there are/were good Jesuits) writes:
PROCESSION, the origin of one from another. A procession is said to be external when the terminus of the procession goes outside the principle or source from which it proceeds. Thus creatures proceed by external procession from the triune God, their Primary Origin. An internal procession is immanent; the one proceeding remains united with the one from whom he or she proceeds. Thus the processions of the Son and the Holy Spirit are an immanent act of the Holy Trinity. An internal, divine procession signifies the origin of a divine person from another divine person (Son from the Father), or from other divine persons (the Holy Spirit from the Father and the Son) through the communication of numerically and the same divine essence.
I am not going to go into the Filioque Controversy which produced the Great Schism of the Sixth Century. One can find a lot about it on Google.