The purpose of icons is first to create reverence in worship and second to serve as an existential link between the worshipper and God. The icon is a link between the human and the divine. It provides a space for the mystical encounter between the person before it and God.
In the icons very little room is made for artistic license. Almost everything within the image has a symbolic aspect. Christ, the saints, and the angels all have halos. Angels have wings because they are messengers. Figures have consistent facial appearances, hold attributes personal to them, and use a few conventional poses.
Colour too plays an important role. Gold represents the radiance of Heaven; red, divine life. Blue is the colour of human life, white is the uncreated essence of God, only used for resurrection and transfiguration of Christ. Letters are symbols too. Most icons incorporate some calligraphic text naming the person or event depicted. Even this is often presented in a stylized manner.
In the Eastern Orthodox Christian tradition there are reports of particular icons that perform miracles upon petition by believers. When such reports are verified by the Orthodox hierarchy, they are understood as miracles performed by God through the prayers of the saint, rather than being magical properties of the painted wood itself. Theologically, all icons are considered to be sacred, and are miraculous by nature, being a means of spiritual communion between the heavenly and earthly realms. However, it is not uncommon for specific icons to be characterised as "miracle-working", meaning that God has chosen to glorify them by working miracles through them. Such icons are often given particular names (especially those of the Virgin Mary), and even taken from city to city where believers gather to venerate them and pray before them.