When Mary was told she would be with child, and this baby was to be none other than God, she was curious how this would happen. She was told she would become pregnant via the Holy Spirit's power. From that time she carried the Christ within her.
Many Christian groups around the world, such as Catholics and Orthodox, plus our early church fathers had a title for Mary, naming her the Theotokos. This means the bearer of God. When the Holy Spirit came on Mary, she carried God within her. Thus she was pregnant, and gave birth to Jesus, who was called Immanuel which means "God is with us."
Both the prediction of Mary giving birth, and of God being with us come from Isaiah chapter 7, which Matthew reminds us of in chapter 1 of his gospel.
Although Mary has an elevated status in the mind of many believers, especially more traditional Christians, it was not her power or ability which caused her to carry God within. But her faith, and willingness made it possible for God to do what was miraculous.
Later in the gospels Jesus said, "anyone who does my will, is my brother or sister or mother." (Mark 3:35) Jesus knew that for any of his followers, being willing and having faith puts us on the same level as Mary, his physical mother.
Many a teenage christian girl has wondered what it would have been like to have carried Jesus within. Once during a youth meeting I asked them all the young ladies, who unanimously affirmed that desire. Yet the opportunity to carry Christ within is available to all believers, both female and male.
Every sincere believer who seeks God for the Holy Spirit will receive a portion of God within. So when the spirit comes upon you, you also will carry God inside of you. You will become, as Mary was, the bearer of God. You also are a Theotokos.
This Christmas remember that the God who came into the world is Immanuel, God with us. This God wants to be with you in such a way that it changes your existence and reality. You are to walk with God and have His presence with you. God also wants to be in the world, and with its people because he is in the world through you. You are to be Christ to all of those around you. These are the things that we are reminded of at the time of the Advent, that is Christmas.
If you do love God, then you carry him. Allow your light to shine, so that your deeds glorify God before others.