“Tell me, O blessed Mary, whom did you conceive in your virginal womb? Yes, even the firstborn Word of God, who came down from heaven into you and was formed, the firstborn man, in your womb, so that the firstborn Word of God might appear united with the firstborn man.”
Hippolytus, Eranistes, Dial. 1: PG 83,88
Believing that Jesus was born of a virgin is the Only-Begotten Son-of-God, and the firstborn qualified Him as the Saviour of the world.
N.B. ‘qualified’ does not fully explain the extent of why Jesus is the Only saviour of the world.
If you are interested in more quotes on Virgin Mary, you can find them in Mary and the Fathers of the Church on Amazon in both in Kindle and paperback formats.
References:
Gambero, L., 1999. Mary and the Fathers of the Church 1st ed. Translated by Buffer, T., San Francisco: Ignatius Press.p.88