What if Mary had said "No"?

Readings for the Fourth Sunday of Advent (Year A) 22nd December 2019.

Reading 1

Isa 7:10-14

The maiden is with child.

Psalm

Ps 23:1-2, 3-4, 5-6

Let the Lord enter! He is the king of glory.

Reading 2

Rom 1:1-7

Jesus Christ, descendant of David, Son of God.

Gospel

Matt 1:18-24

Jesus is born of Mary`who was betrothed to Joseph, son of David.