Luke 1:34-38

Faith alone pleases God. When we act in faith even when we don’t fully understand all the details to what the Holy Spirit reveals to us we are blessed.  We cannot let fear of misunderstanding Him stop us from doing what He calls us to do. His mercy and grace follow us on His path of redemption. With Him all things are possible!

Mary did not ask for a sign, so this remark does not reflect unbelief. She accepts her role without question, and thus is a model of faith even though she does not fully understand everything. The work of God in Mary introduces something unknown before or after: the birth into the human race of One who is both God and man. 
This is a direct declaration of Jesus’ divine conception. 

God keeps His promises regardless of how difficult the circumstances may seem. Gabriel’s statement about God should be our statement of faith: Nothing is impossible with God.

Luke 1:34-38

³⁴ Then Mary said to the angel, “How can this be, since I do not know a man?” 

³⁵ 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. ³⁶ 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. ³⁷ For with God nothing will be impossible.” 

³⁸ Then Mary said, “Behold the maidservant of the Lord! Let it be to me according to your word.” And the angel departed from her.