"How can this be?"
Mary's question about Christmas can be answered by God's love. It can also be answered by God's power. If God made whole universe then He is obviously is very powerful. If He made the cosmos, He also made all the laws of physics, biology, etc. So He knows how to use those laws and even bypass them to accomplish His purpose. The angel Gabriel, when asked by Mary how she could become pregnant since she was a virgin, answered that "the Holy Spirit shall come upon you, and the power of the most high will overshadow you."(Lk. 1:35) God's motive for the incarnation was love and His agent for it was His power.
It is hard for us to conceive of a time when there was nothing(not even time)--except God Himself. Out of this emptiness the Spirit of God was moving and the Father was speaking the the world into existence through His Son. Where there was darkness, there now was light--simply done by the Word of God. Think of the vastness of the universe--the unimaginable distances to other stars and galaxies--and the micro distances as we study particles so small that no telescope can detect them--physicists only assume that they must exist. God is bigger than all of that!
Our God is a god of the supernatural--a God of miracles. Three great miracles mark history. These great supernatural acts of God are the creation, the incarnation, and the resurrection.
If God can do all that, He can do a miracle in your life. Your life may be empty--let the Spirit of God hover over you and come upon you. Your life may be dark and you can't find your way or you need guidance--let God speak light into your life through His Son who is the Light of the world.
When I say, "let God", I mean trust Him to do what He promises He will do. Gabriel told Mary, "nothing is impossible with God." (Lk. 1:37) Literally that means, no word from God is without power. Just as Mary believed the word of God and surrendered to it, so we can believe His promise (His Word who is the Word) and in surrendering to Him have a supernatural Christma