These three persons are distinguished by their relationship to one another. The Father is eternal and uncreated and proceeds from no one. The Son is eternal and proceeds from the Father. The Holy Spirit is eternal and proceeds from the Father (and not "from the Father and the Son" as in Catholicism - a divergence between Orthodoxy and Catholicism).
God is one in three Persons. In God, there is a unity of nature and essence, but a triplicity of Persons: Father, Son and Holy Spirit. The incarnate Jesus Christ is true God and true man. In him is all the fullness of divinity and humanity.
