The Trinity (Father, Son and Holy Spirit)
Orthodox Christians worship the Father, Son and Holy Spirit-the Holy Trinity, the one God. Following the Holy Scriptures and the Church Fathers, the Church believes that the Trinity is three divine persons (hypostases) who share one essence (ousia). It is paradoxical to believe thus, but that is how God has revealed himself. All three persons are consubstantial with each other, that is, they are of one essence (homoousios) and coeternal. There never was a time when any of the persons of the Trinity did not exist. God is beyond and before time and yet acts within time, moving and speaking within history.
God is not an impersonal essence or mere "higher power," but rather each of the divine persons relates to mankind personally. Neither is God a simple name for three gods (i.e., polytheism), but rather the Orthodox faith is monotheist and yet Trinitarian. The God of the Orthodox Christian Church is the God of Abraham, Isaac and Jacob, the I AM who revealed himself to Moses in the burning bush.
The source and unity of the Holy Trinity is the Father, from whom the Son is begotten and also from whom the Spirit proceeds. Thus, the Father is both the ground of unity of the Trinity and also of distinction. To try to comprehend unbegottenness (Father), begottenness (Son), or procession (Holy Spirit) leads to insanity, says the holy Gregory the Theologian, and so the Church approaches God in divine mystery, approaching God apophatically, being content to encounter God personally and yet realize the inadequacy of the human mind to comprehend him.
The primary statement of what the Church believes about God is to be found in the Nicene - Constantinopolitan Creed:
"I believe in one God, the Father Almighty, Maker of Heaven and Earth and of all things visible and invisible. And in the Lord Jesus Christ, the Son of God, the only-begotten, begotten of the Father before all ages. Light of light; true God of true God; begotten, not made; of one essence with the Father, by Whom all things were made; Who for us men and for our salvation came down from Heaven, and was incarnate of the Holy Spirit and the Virgin Mary, and became man. And He was crucified for us under Pontius Pilate, and suffered, and was buried. And the third day He arose again, according to the Scriptures, and ascended into Heaven, and sits at the right hand of the Father; and He shall come again with glory to judge the living and the dead; Whose Kingdom shall have no end. And in the Holy Spirit, the Lord, the Giver of Life, Who proceeds from the Father; Who with the Father and the Son together is worshiped and glorified; Who spoke by the prophets. In one Holy, Catholic, and Apostolic Church. I acknowledge one baptism for the remission of sins. I look for the resurrection of the dead and the life of the world to come. Amen"