The icon is an integral part of not only Russian culture, but also of Europe during the Middle Ages, which had a different chronological timeline than in Russia.
Unlike Western European countries, Russian art skipped the Renaissance. The Middle Ages in Russia lasted from the end of the 10th century, when early Russia adopted Christianity, until the turn of the 17th and 18th centuries, when Peter I ascended the throne and channeled the country's culture in a different direction. However, the development of the icon never stopped and later icons and holy pictures were painted for new churches, where you could find traces of Baroque and Rococo art, classicism and Art Nouveau.
Nevertheless, the basic principles evolved during those seven earlier centuries, when ecclesiastical art prevailed over its secular counterpart.