The Orthodox Church teaches that we have knowledge of God, only because God has shown himself to his creation. God is the Lord and has revealed himself unto us; blessed is he who comes in the name of the Lord (Ps 118:26-27). Also, God's self-revelation is found in His Son Jesus Christ, the fulfillment of the gradual and partial revelation of God in the Old Testament. Jesus is the one truly "blessed ... who comes in the name of the Lord."
God is holy
According to the Scriptures, and the experience of the saints of both the old and New Testaments, God is absolutely holy. This means literally that he is absolutely different and unlike anything or anyone else that exists. He is so unique and so perfect that his existence cannot be compared to any other existence. God is absolutely transcendent, "what he is, by essence and nature, is altogether beyond our comprehension and knowledge" (John of Damascus) .
One God, the Holy Trinity
Orthodox doctrine holds that God's unity or oneness is also not merely the mathematical or philosophical concept of "one". The Church teaches God as the Trinity. One God, three persons, Father, Son, And Holy Spirit, each of whom ‘dwells' in the other two, by virtue of a perpetual movement of love. God is not only a unity but a union.
It is the Church's teaching and its deepest experience that there is only one God because there is only one Father. The Son is born from the Father, and the Spirit proceeds from the Father, both in the same timeless and eternal action of the Father's own being. What the Father is, the Son and the Spirit are also. They share the divine nature with God the Father, being "of one essence" with him.
Just as the Father is "ineffable, inconceivable, invisible, incomprehensible, ever-existing and eternally the same" (Divine Liturgy of St. John Chrysostom), so the Son and the Spirit are exactly the same. Every attribute of divinity which belongs to God the Father: life, love, wisdom, truth, blessedness, holiness, power, purity, and joy, belong equally as well to the Son and the Holy Spirit.
In the Bible the term "God" with very few exceptions is used primarily as a name for God the Father. Thus, the Son is the "Son of God," and the Spirit is the "Spirit of God."
It is God, the Yahweh of Israel (the God of Abraham, Isaac, and Jacob) , whom Jesus Christ has claimed to be his Father. God Almighty is known as "Father" through his son Jesus Christ. Jesus taught man to call the Almighty God by the title of Father. Before Jesus no one dared to pray to God with the intimate name of Father. It was Jesus who said, "Pray like this: Our Father who art in heaven ..."
Maker of Heaven and Earth
The Orthodox doctrine of creation is that God has brought everything and everyone which exists from non-existence into being. The scriptural description of creation is given primarily in the first chapter of Genesis. The main doctrinal point about creation is that God alone is uncreated and ever-existing. Everything which exists besides God was created by him.
God is everywhere
The omnipresence of God is one of the divine attributes of the Creator particularly stressed in Church teachings. Loving the whole of his good creation, God dwells within the world that he has made because of his goodness and love for man. This is not to say that God "is" his creation, for he is more than that, God is above and outside his creation, yet he also exists within it.
We don't know God by his essence and nature, but his energies come down to us. God's energies, which are God himself, permeate all his creation, and we experience them in the form of deifying grace and divine light. Truly our God is a God who acts in history, intervening directly in concrete situations.
God has come down to man, not only through his energies, but in his own person. The second person of the Trinity, ‘true God from true God,' was made man: "The Word became flesh and dwelt among us" (John 1:14).
This Incarnation of the Son, the Wisdom of God, as the Son of Man, is Jesus Christ.