Q241
How do we know that the Holy Spirit proceeds from the Father?
Concerning the procession of the Holy Spirit, the Orthodox faith has received, and confesses without addition, the very words of the Lord himself: the Spirit of Truth “proceeds from the Father” (Joh 15:26; see Q094, Q243). The Creed simply repeats this word of the Gospel. The Lord’s words are these:
But when the Comforter has come, whom I will send to you from the Father, the Spirit of Truth, who proceeds from the Father, he shall testify of me (Joh 15:26).
There are two distinct verbs: the Son sends the Spirit in time (the economy); the Spirit proceeds from the Father eternally (the ontology).