St. Theophilus of Antioch on the Energetic Procession of the Holy Spirit
St. Theophilus of Antioch, cited by Thomas Aquinas in “Catena Aurea”, Commentary on John 15:26: “But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me:”
Elsewhere He says that the Father sends the Spirit; now He says He does: Whom I will send to you, thus declaring the equality of the Father and the Son. That He might not be thought however to be opposed to the Father, and to be another and rival source, as it were, of the Spirit, He adds, From the Father, i.e., the Father agreeing, and taking an equal part in sending Him. When it is said that He proceeds, do not understand His procession to be an external mission, such as is given to ministering spirits, but a certain peculiar, and distinct procession, such as is true of the Holy Spirit alone. To proceed is not the same as being sent, but is the essential nature of the Holy Ghost, as coming from the Father.
St. Theophilus makes a very critical distinction between the procession of the Holy Spirit, which is proper from the Father alone, and the sending of the Holy Spirit, which is from the Father and (or through) the Son. He then distinguishes the eternal procession, which is the eternal causation of the Holy Spirit, from the temporal sending of the Holy Spirit, saying one is from the Father, the other from the Father and the Son. Roman Catholics typically tend to confuse theology and economy and say the double sending from the Father and the Son indicates the double hypostatic procession, but St. Theophilus alongside many other fathers such as St. John of Damascus rejects such an idea.
The procession from the Father is the “essential nature” of the Holy Spirit, in the sense that this is proper to Him alone in distinction with the other Divine persons in the Trinity. This points out what we call “hypostatic property”, while the Holy Spirit has everything in common with the Father and the Son, His procession from the Father is what is true to Him alone.