In the Orthodox Church the terms “Mystery” or “The Mysteries” refer to the process of theosis. While it is understood that God theoretically can do anything instantly and invisibly, it is also understood that he generally chooses to use material substance as a medium in order to reach people. The limitations are those of mankind, not God. Matter is not considered to be evil by the Orthodox. Water, oil, bread, wine, etc., all are means by which God reaches out to allow people to draw closer to him. How this process works is a “Mystery”, and cannot be defined in human terms. These Mysteries are surrounded by prayer and symbolism so that their true meaning will not be forgotten.

Those things which in the West are often termed Sacraments or sacramentals are known among the Orthodox as the Sacred Mysteries. While the Roman Catholic Church numbers seven Sacraments, and many Protestant groups list two (Baptism and the Eucharist) or even none, the Orthodox do not limit the number. However, for the sake of convenience, catechisms will often speak of the seven Great Mysteries. Among these are Holy Communion (the most direct connection), Baptism, Chrismation, Confession, Unction, Matrimony, and Ordination. But the term also properly applies to other sacred actions such as monastic Tonsure or the blessing of holy water, and involves fasting, almsgiving, or an act as simple as lighting a candle, burning incense, praying or asking God's blessing on food.