Youcat commented through CCC - Question n. 80 - Part X.

YOUCAT Question n. 80 - Part X. Why is Mary a Virgin?

(Youcat answer - repeated) God willed that Jesus Christ should have a true human mother but only God himself as his Father, because he wanted to make a new beginning that could be credited to him alone and not to earthly forces.       

A deepening through CCC

(CCC 497) The Gospel accounts understand the virginal conception of Jesus as a divine work that surpasses all human understanding and possibility: (Mt 1 18-25; Lk 1:26-38) "That which is conceived in her is of the Holy Spirit", said the angel to Joseph about Mary his fiancée (Mt 1:20). The Church sees here the fulfillment of the divine promise given through the prophet Isaiah: "Behold, a virgin shall conceive and bear a son" (Isa 7:14 (LXX), quoted in Mt 1:23 (Gk). (CCC 504) Jesus is conceived by the Holy Spirit in the Virgin Mary's womb because he is the New Adam, who inaugurates the new creation: "The first man was from the earth, a man of dust; the second man is from heaven" (1 Cor 15:45, 47). From his conception, Christ's humanity is filled with the Holy Spirit, for God "gives him the Spirit without measure" (Jn 3:34). From "his fullness" as the head of redeemed humanity "we have all received, grace upon grace" (Jn 1:16; cf. Col 1:18).   

Reflecting and meditating 

(Youcat comment) Mary’s virginity is not some outdated mythological notion but rather fundamental to the life of Jesus. He was born of a woman but had no human father. Jesus Christ is a new beginning in the world that has been instituted from on high. In the Gospel of Luke, Mary asks the angel, “How can this be, since I have no husband?” ( do not sleep with a man, Lk 1:34); the angel answered, “The Holy Spirit will come upon you” (Lk 1:35). Although the Church from the earliest days was mocked on account of her belief in Mary’s virginity, she has always believed that her virginity is real and not merely symbolic.    

(CCC Comment)

(CCC 508) From among the descendants of Eve, God chose the Virgin Mary to be the mother of his Son. "Full of grace", Mary is "the most excellent fruit of redemption" (SC 103): from the first instant of her conception, she was totally preserved from the stain of original sin and she remained pure from all personal sin throughout her life.      

(The next question is: Did Mary have other children besides Jesus?)