An iconostasis is a wall of icons, separating the nave from the sanctuary of the church. This for orthodox churches typical wall of icons is also shown in both St. Nicholas Churches in the Abbey of Niederaltaich.

The iconostasis typically has three doors, the Holy Doors in the center and  the West and East Doors on each side and shows icons above and besides all doors. In orthoodx churches, iconostasis is seen as a symbol of bonding between heaven and the nave. Therefore, the Iconostasis does not really"separate" the nave from the Holy of Holies, it rather brings them together.

In the big St. Nicholas Church, there is a Deisis above the Holy Doors, which ist the main part of the iconostasis. In the center of the Deisis is a large icon of Christ Enthroned , to his right an icon of the Theotokos (Virgin Mary) and to the left an icon of  John the Baptist . They are  flanked by icons of different saints, all of them in attitudes of supplication. Above the West and the East Doors, the icons of the Twelve Great Feasts are shown.

In the spirituality and theology of the Eastern Churches, Icons play a very important role.
An icon (Greek: image) is a picture or representation of  a holy being or object, such as Jesus, Mary, saints or angels. Although being a picture, the worshiping of icons in the Eastern Churches is never dedicated to the picture itself, but to person represented through the icon.