In the time of Jesus, a widow who had no close male relative to look after her faced a precarious existence. By entrusting Mary to the “beloved disciple” (commonly understood to be John), Jesus was showing love and concern for his mother, ensuring that she would be safe and cared for after his death.
Additionally, the Catholic Church has always seen this as a defining moment in the role of Mary in the Church. With the words, “Woman, behold, your son” and “Behold, your mother,” the Church teaches that Mary became the mother not just of John, but of all believers. Pope John Paul II reflected on this belief in his 1987 encyclical letter Redemptoris Mater:
“The words uttered by Jesus from the Cross signify that the motherhood of her who bore Christ finds a ‘new’ continuation in the Church and through the Church, symbolized and represented by John … In accordance with the eternal plan of Providence, Mary’s divine motherhood is to be poured out upon the Church, as indicated by statements of Tradition, according to which Mary’s ‘motherhood’ of the Church is the reflection and extension of her motherhood of the Son of God.”
So when Catholics refer to Mary as “our mother,” it goes back to this moment in Scripture. Just as Jesus designated Mary as the mother of John, Catholics believe that she looks after all of us as well through her prayers and her love.
Editor’s note: Several scripture scholars have also surmised that the author of John’s Gospel used the term “beloved disciple” as a literary device, not meant to refer to an actual person but rather, to each reader of the gospel. In this manner the beloved disciple is “us” and thus Mary is given to all.