By faith, Mary accepted the Angel’s word.
‘Yes, blessed is she who believed that the promise made her by the LORD would be fulfilled.’
Elizabeth says Mary is blessed/ happy because she believed. And what did Mary believe? Mary knew fully that God had called her to a real virginal marriage. At the angel’s word, she moved very rapidly to a new fullness of the knowledge that she would also be Mother of the Son of the Most High. In Her fullness of knowledge, she also knew that nothing is impossible to God. She inquired for this knowledge to be revealed and the revelation was that even though Joseph was spouse, he was creature and therefore incapable of generating a Divine Person, even though he was true father by virtue of being one body with her.
In the beginning when God created the heavens and the earth, he sent forth his Creating Spirit. With the Spirit, he also sent His Son, by whom everything was created and for whom (The Son) everything was created.
It is the fullness of time and the Divine Person, the Spirit, sent by the Father and the Son, and ‘carrying the Son’, is ready to deliver the Word fully in the body he forms in Mary’s womb and is waiting on her fiat!
With her fiat! Mary did the will of the LORD’s Father in heaven and became his Mother.
Elizabeth says Mary is blessed/ happy for believing, but she is ‘still happier for hearing the Word of God and keeping it!’
And the sign she kept it was shown in love for neighbor: ‘Mary set out at that time and went as quickly as she could to a town in the hill country of Judah.’
 Cf. Lk1:37
 Cf. Heb7:10
 Cf. Lk2:48
 Cf. Gn1:1
 Cf. Gn1:2
 Cf. Col1:16
 Cf. Col2:9
 Cf. Mt. 12:50
 Cf. Lk11:28