Now in the sixth month the angel Gabriel was sent by God to a city of Galilee named Nazareth, to a virgin betrothed to a man whose name was Joseph, of the house of David. The virgin’s name was Mary.
And having come in, the angel said to her, “Rejoice, highly favored one, the Lord is with you; blessed are you among women!”
But when she saw him, she was troubled at his saying, and considered what manner of greeting this was. Then the angel said to her, “Do not be afraid, Mary, for you have found favor with God. And behold, you will conceive in your womb and bring forth a Son, and shall call His name JESUS. He will be great, and will be called the Son of the Highest; and the Lord God will give Him the throne of His father David. And He will reign over the house of Jacob forever, and of His kingdom there will be no end.” (Luke 1:26-33)
Imagine being confronted with a similar issue. Doesn't need to be about bearing a child! What if God was calling you to be His child!? It was an announcement.
Then Mary said to the angel, “How can this be, since I do not know a man?” And the angel answered and said to her, “The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God. Now indeed, Elizabeth your relative has also conceived a son in her old age; and this is now the sixth month for her who was called barren. For with God nothing will be impossible.” Then Mary said, “Behold the maidservant of the Lord! Let it be to me according to your word.” And the angel departed from her. (Luke 1:34-38)
Mary heard, she understood, she wondered how. But she made a crucial decision. She didn't fully grasp the enormity of it all yet, but she knew she had been confronted by a messenger of God. She accepted.
It's not much different than God calling us, choosing us...to become His child. We should consider it a blessing and rejoice at His urging.
Mary hadn't known a man, in the physical context. We do not know the Man, Jesus, in a spiritual way, until we receive the power of the Holy Spirit, to be born of the Spirit. But first we need to respond as Mary did: Let (this new life in Christ with His Spirit within me) be to me according to your word.
Being born of the Spirit. Being overpowered by the Son of God Himself. Nothing is impossible with God. Do you realize the privilege of having God living inside? Mary knew in one sense. So can we in another. Christ in me, the hope of glory. It's never too late to allow this to happen. He is always calling; He is always sending a messenger.