The icon of the Mother of God, More Spacious Than the Heavens, is found on the wall above and behind the Altar in most Orthodox Churches. This icon shows Mary interceding for the universe with Christ inside her (in some versions of this icon, Christ is surrounded by a circle of sorts, indicating that He can only be seen by faith). So in a mystery, Christ God in the heart/womb of Mary intercedes through Her to the Father on behalf of the universe. And more than that, because Christ already holds the universe in his hand (according to the Psalmist) and holds all things together by the Word of His Power (according to St. Paul), within Mary already is the whole universe. Thus we call Her More Spacious Than The Heavens because she held in Her womb Him who holds the whole universe.
However, in another mystery, Mary is a type or symbol of the whole Church in whom Christ dwells. And at the Divine Liturgy of the Church, like Mary, the Church bearing Christ in its heart–in the hearts of all the faithful–intercedes for the universe. Or Christ through the Church intercedes to the Father. This is one of the reasons why the icon is placed where it is in the Apse (the curved dome above and behind the Altar) of the Church.
Christ in taking on human nature has so united Himself to mankind that He abides (dwells, lives, tabernacles) in the hearts of men and women who draw near to him through faith. St. Paul likens this reality to both a marriage and an adoption. By Christ’s dwelling in our hearts, we mere creatures are made partakers of the Divine, for Christ’s humanity and divinity cannot be separated. Just as in marriage or adoption someone becomes a member of a new family, so in baptism through faith we become members of God’s family–not distant relatives, but as close as a wife or son.
And as Christ ever lives to make intercession, so those in whom Christ dwells also ever live to make intercession. And the first Christian, the first to hold Christ in Her heart, Mary His Mother, is the pattern, the prototype of the Christian people. In Christ She ever intercedes for us that we too might have Christ dwelling in our hearts by faith and ever learn to intercede.