"Everyone has a mother. Yes, the mother who gave them birth in the physical order of life. But Christian believers have another mother, the Blessed Virgin Mary, in the spiritual order of grace. Jesus willed to give Mary as a mother to the early Church, when, from the cross, he looked at his mother and said, “Woman, behold, your son” (John 19:26). And to the beloved disciple, “Behold, your mother” (John 19:27)." (http://www.catholicdigest.com/faith/spirituality/mother-of-the-church/)
The Apostle Paul tells us in Galatians 4:26 that the heavenly Jerusalem is the mother of the church:
"But the Jerusalem above is free; she is our mother."
In that same context, the virgin birth is alluded to and Mary is only described as a woman:
"But when the fullness of the time came, God sent His Son, born of a woman, born under the Law." (Galatians 4:4)
In his epistle to the Romans, Paul mentioned Rufus' mother and said that she had been a motherly figure to him:
"Greet Rufus, a choice man in the Lord, also his mother and mine." (Romans 16:13)
If Mary is the mother of the church, then it is ironic that he says nothing about Mary.
The Apostle John says nothing about Mary in his letters to the churches and mentions her only twice in his gospel (the wedding at Cana and the crucifixion of Jesus). This is significant because he took Mary into his home after Jesus was crucified.
John was the disciple who Jesus loved (John 21:20). He was present at His crucifixion. Because John believed Christ to be the Son of God, he was considered a part of the true family of God (Luke 8:21). Christ's blood brothers did not believe at that point in time and hence were not a part of His true family (John 7:5). That is why Christ handing His mother Mary to John for care rather than one of His blood brothers can be viewed as appropriate. In so doing, He was being faithful to both the letter and spirit of the Law.
"The Fathers of the Church and early Christian writers did not so interpret the words of the dying Christ [John 19:25-27]. Development of the idea of Mary's spiritual motherhood was slow and did not enter the consciousnesses of the Church until medieval times. During those early centuries, the sacred text did not immediately convey the notion. Lengthy reflection was needed to reach it." (Michael O'Carroll, cited in Cult of the Virgin: Catholic Mariology and the Apparitions of Mary, Elliot Miller and Kenneth R. Samples, p. 44)
