Many icons depict Mary with the infant Jesus. You will often see Theotokos, a Greek title for Mary, associated with icons of this nature. A title literally means God-bearer or Mother of God. Many of us who grew up outside of the Orthodox and Roman Catholic traditions are uneasy about using language of this nature about Mary. It can feel like we are coming dangerously close to Mariolatry, the worship of Mary. Personally, learning the history around this title for Mary has helped me move past my uneasiness in this area.
Some Christians at that time were advocating the title Christotokos or Christ-bearer. For them, the idea that the eternal God could be born of a woman made no sense. Yes, they could affirm Jesus as Christ and that the Jesus who died on the cross was human and divine. But to them there must be some distinction between the human nature of Jesus and the divine nature of Christ. These two natures could not be one in the same. To them, the practice of calling Mary Theotokos was saying that the Jesus Mary carried in her womb was both fully human and fully God and therefore misrepresented who Jesus is.
"What is the relationship between the divine and human nature of Jesus?" Orthodox, Roman Catholic, Anglican and many other Christians are in agreement about this. Mary did not bear an ordinary human child. Jesus was fully God and fully human as a babe in Mary's womb. She is therefore appropriately called the "Mother of God." Her babe is completely divine just as God the Father and God the Spirit are completely divine. Her babe is completely human--exactly like you and me except without sin.
I could say much more on the theology of this icon but in many ways that is missing the point. Icons are not "doctrine in pictorial form." They are windows into the mysteries of our faith. Jim Forest, author of "Praying with Icons," list among the qualities of icons are an aid to worship. In other words they are meant to be in Churches and used in the devotional life of Christians. They are not meant to be works of art in a museum or to be critically analyzed for the meaning of every color and brushstroke. They call us into deeper relationship with God through prayer. Any yet, this icon and the famous Trinity icon below do draw me prayerfully into those two questions of the first four councils. They draw me into the mystery of the Trinity and the mystery of the Incarnation. That is why if you walk into my office you will see them hanging from the wall behind my computer screen.
To the right is Rublev's Trinity icon. It refers to the story of Abraham and Sarah's hospitality to three nameless strangers by the oaks of Mamre near Hebron. During their visit they promise that the aged Sarah will bear a Son. Early Christians saw these three strangers as a revelation of the Trinity. Andrei Rublev wrote (ie painted) this version of the icon around 1425.