Handbook of Liturgical Practice of the Russian Church Abroad
Prior to the Royal Doors being opened and the Chalice being brought out by the Deacon and Priest, the faithful will often form a queue to venerate the principal icon of the day, found to the right side of the amvon, or else the icons of Christ and the Theotokos. This practice dates back to the time of the iconoclastic controversy in the seventh and eighth centuries, when many so-called Christians denied the sanctity of the holy icons and the propriety of their veneration; for this reason, venerating the icons before communing became a kind of ‘confession of faith,’ demonstrating that one rightly believed (i.e. was Orthodox) and therefore could be admitted to the chalice. The practice remains even today as a sign of piety.
However, once the Royal Doors have been opened and the Chalice brought out, it is strictly forbidden to venerate any icons. This is because icons always point towards Christ, while in the Chalice is present before us Christ Himself — not an icon, but His own immediate presence. We often observe faithful continuing to venerate icons as they wait in the queue to come up to the Chalice; this is a terrible habit and should be stopped immediately, through a right education of the faithful by the clergy, so that we always show pious reverence to Christ ‘in our midst’ in the Holy Gifts.