Whereas orthodox Christology holds that Christ has two natures, divine and human, ineffably united in one person, or hypostasis, Nestorianism so stresses their independence as to suggest that they are in effect two persons, or hypostases, loosely joined by a moral union.
once he was not, or he was not before his generation, or he came to be out of nothing, or…he, the Son of God, is of a different hypostasis or ousia [Greek: "essence"], or that he is a creature, or changeable or mutable.
And his account of the emanation process avoids the many difficulties that had puzzled Neoplatonists as they tried to understand how the second hypostasis (reality) proceeds from the One.
The Cappadocian Fathers (Gregory of Nyssa, Gregory of Nazianzus, and Basil of Caesarea) were even accused of being tri-theists because of their conception of God as one essence in three hypostases (the Greek term hypostasis was the equivalent of the Latin substantia and designated a concrete reality).
Uniting himself with this soul, the divine Logos, who is the second hypostasis (Person) of the triad of Father, Son, and Spirit (subordinate to the Father but on the divine side of the gulf between infinite Creator and finite creation), became incarnate in a body derived from the Virgin Mary.
Most famously, the song "Lekhah dodi" ("Let Us Walk, My Love"), which greets the arrival of the feminine hypostasis, was composed by mystics in the town of Ẕefat in Upper Galilee.
A reaction led by Pope Leo I (reigned 440 461) against this one-nature (Monophysite) doctrine culminated in the Council of Chalcedon (451), which affirmed Christ to be two natures in one person (hypostasis).
This power is also the divine "Presence" (Shekhina) of rabbinical theology, though it is profoundly transformed: it has become a hypostasis.
The key ideas of these Christological and Trinitarian debates and their conclusions were based upon the Greek concepts of ousia (nature or essence) and hypostasis (entity, used as virtually equivalent to prosōpon, person).
The Nicene Creed states that Jesus is The council rejected the opinion of those who argued, as Eusebius put it in a famous letter, that once he was not, or he was not before his generation, or he came to be out of nothing, or…he, the Son of God, is of a different hypostasis or ousia [Greek: "essence"], or that he is a creature, or changeable or mutable.
In Hellenic philosophy "ipostas" or "hypostasis" is taken to signify the underlining, inner reality of things.
