Pneumatology is the study of spiritual beings and phenomena, especially the interactions between humans and God. Pneuma (πνευμα) is Greek for "breath", which metaphorically describes a non-material being or influence. World Book Dictionary defines pneumatology as "1. Theology the doctrine of the Holy Spirit. 2. The doctrine of spirits or spiritual beings, in the 1600s considered a branch of metaphysics. 3. pneumatics. 4. Obsolete word for psychology."
In Christian theology pneumatology refers to the study of the Holy Spirit. In mainstream Christian doctrine, the Holy Spirit is the third person of God in the Trinity. Unitarian forms of Christianity believe that the Holy Spirit is personal, although holding that it may, in some sense, influence people. In the Gospel of John, pneuma is linked to re-birth in water and spirit, which has been suggested to be baptism.
 The pneumatology of Philo
Philo (20 B.C. - A.D. 40) was an Alexandrian Jewish philosopher known for his study of pneumatology. He treats God's divine powers by treating them as a single independent being, which he designates "Logos". This name, which he borrowed from Greek philosophy, was first used by Heraclitus and then adopted by the Stoics. Philo's conception of the Logos is influenced by both of these schools. From Heraclitus he borrowed the conception of the "dividing Logos" (λόγος τομεύς), which calls the various objects into existence by the combination of contrasts, and from Stoicism, the characterization of the Logos as the active and vivifying power.
Philo borrowed also Platonic elements in designating the Logos as the "idea of ideas" and the "archetypal idea". There are, in addition, Biblical elements: there are Biblical passages in which the word of YHWH is regarded as a power acting independently and existing by itself, as Isaiah lv. 11; these ideas were further developed by later Judaism in the doctrines of the Divine Word creating the world, the divine throne-chariot and its cherub, the divine splendor and its shekinah, and the name of God as well as the names of the angels; and Philo borrowed from all these in elaborating his doctrine of the Logos.
Philo calls the Logos the "archangel of many names," "taxiarch" (corps-commander), the "name of God," also the "heavenly Adam", the "man, the word of the eternal God." The Logos is also designated as "high priest," in reference to the exalted position which the high priest occupied after the Exile as the real center of the Jewish state. The Logos, like the high priest, is the expiator of sins, and the mediator and advocate for men. From Alexandrian theology Philo borrowed the idea of wisdom as the mediator; he thereby somewhat confused his doctrine of the Logos, regarding wisdom as the higher principle from which the Logos proceeds, and again coordinating it with the latter.
 Relation of the Logos to God
Philo, in connecting his doctrine of the Logos with Scripture, first of all bases on Genesis 1:27 the relation of the Logos to God. He translates this passage as follows: "He made man after the image of God," concluding therefrom that an image of God existed. This image of God is the type for all other things (the "Archetypal Idea" of Plato), a seal impressed upon things. The Logos is a kind of shadow cast by God, having the outlines but not the blinding light of the Divine Being.
The relation of the Logos to the divine powers, especially to the two fundamental powers, must now be examined. And here is found a twofold series of exegetic expositions. According to one, the Logos stands higher than the two powers; according to the other, it is in a way the product of the two powers; similarly it occasionally appears as the chief and leader of the innumerable powers proceeding from the primal powers, and again as the aggregate or product of them. In its relation to the world the Logos appears as the Universal substance on which all things depend; and from this point of view the manna (as γενικώτατόν τι) becomes a symbol for it.
The Logos, however, is not only the archetype of things, but also the power that produces them, appearing as such especially under the name of the Logos τομεύς ("the divider"). It separates the individual beings of nature from one another according to their characteristics; but, on the other hand, it constitutes the bond connecting the individual creatures, uniting their spiritual and physical attributes. It may be said to have invested itself with the whole world as an indestructible garment. It appears as the director and shepherd of the things in the world in so far as they are in motion. The Logos has a special relation to man. It is the type; man is the copy. The similarity is found in the mind (νοῡς) of man.
For the shaping of his nous, man (earthly man) has the Logos (the "heavenly man") for a pattern. The latter officiates here also as "the divider" (τομεύς), separating and uniting. The Logos as "interpreter" announces God's designs to man, acting in this respect as prophet and priest. As the latter, he softens punishments by making the merciful power stronger than the punitive. The Logos has a special mystic influence upon the human soul, illuminating it and nourishing it with a higher spiritual food, like the manna, of which the smallest piece has the same vitality as the whole.
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