Holy Trinity
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.
--Explanation of the Trinity--
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.
Explanation of the Trinity
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 Trinity Related to Man
Since man is made in the image of God, man also has three natures. Both man and woman have three parts: body, soul, and spirit. God the Son is comparable to the body since the Son is God incarnate. God the Father is comparable to the soul, or mind, since he was the mind that created everything. The Holy Spirit is comparable to man's Spirit. As the body of man is the temple of our spirit, the body of Jesus Christ is the temple to the Holy Spirit which proceeds from the Father through (dia) the Son.
The Trinity Explained in the Creed
The primary statement of what the Church believes about God is to be found in the Nicene-Constantinopolitan Creed.