Stretching out his hand over his disciples, the Lord Christ declared: Here are my mother and my brothers, anyone who does the will of my Father who sent me is my brother and my sister and my mother. I would urge you to ponder these words. Did the Virgin Mary, who believed by faith and conceived by faith, who was the chosen one from whom our Savior was born among men, who was created by Christ before Christ was created in her-- did she not do the will of the Father? Indeed the blessed Mary certainly did the Father's will, and so it was for her a greater thing to have been Christ's disciple than to have been his mother, and she was more blessed in her discipleship than in her motherhood.
A longer excerpt is here, and explains in what sense we too can be mothers of Christ.