Praise be Jesus and Mary, now and forever.
Pentecost is considered the birthday of the Church. Humans are born after nine months of pregnancy. The Church was born after nine days of prayer. The novena that Jesus' disciples prayed as they waited for the descent of the Holy Spirit and prepared themselves for it. St. Luke tells us that after the Ascension the Apostles returned to the upper room and devoted themselves with one accord to prayer together with some women and Mary the mother of Jesus and his brother. So here Mary is the only one named besides the Apostles. Between the Ascension of Jesus on the fortieth day after his resurrection and Pentecost on the fiftieth day after his resurrection, there are nine days. This was the first novena and the model for every other novena. 
And at the center was Mary the mother of Jesus. This is how the iconographic tradition of the Church depicts Pentecost with the Apostles in the upper room gathered around Our Lady. She is at the heart of the Church on the day that it was born, the day of Pentecost. She is the mother of the Church who accompanied it through the period of its gestation and gave birth to it. This is the title, the mother of the Church is the title that St. Paul VI gave her at the end of the third session of Vatican II in 1964. However, the title is much older. We can find it already in the writings of Bernard Bishop of Trier who died in 1125. And after that in other writers such as St. Antoninus, the Bishop of Florence. 
Why is Mary the mother of the Church? First of all, because she is the mother of Jesus as the Acts of the Apostles calls her. The Church is a mystical body as St. Paul teaches. Christ is the head and we are its members. But in any body, the mother of the head is necessarily the mother of the rest of the body. And so Mary is the mother of the mystical body of Christ which is the Church. Consequently, she begins to be the mother of the Church when she begins to be the mother of Jesus at the Annunciation. A further step came when she gave birth to Jesus at Bethlehem. This was a joyful birth, a birth without pain because birth pains are a penalty for original sin and sin had nothing whatever to do with the birth of the Immaculate Son of the Immaculate Mother. 
But when we consider Mary as our mother matters are somewhat different. For here though the mother is still sinless the child is not. We were all conceived in original sin and to that we have added all too many personal sins. So for Mary to give birth to us involves suffering caused by our sins. This is all the more logical because we're talking not about being born physically but about being born by grace to which sin is it directly opposed. This is what Revelation 12:2 is referring to. She was pregnant and was crying out with birth pains in the agony of giving birth. The woman cooked with the Son, the one full of grace, was not in pain at the birth of Christ. You could cite a whole series of fathers of the Church who teach this beginning with Saint Irenaeus at the end of the second century. It is also taught by the magisterium of the Church including Pope Alexander III and the Catechism of Trent.
So if there are pains they are not for Christ's birth but for ours as Saint Pius X and Saint John Paul II teach. Now where did she suffer those pains? Principally at the foot of the cross where the mother of Jesus was standing by her dying son. That is when Jesus, the Word of God said, woman behold your son, and then said to the beloved disciple, behold your mother. That is where she became our mother in regard to the travail of childbirth. For she gives birth to us in the order of grace and the grace by which we live was won principally on the cross. Mary cooperated with Jesus to win that grace, meriting everything that he merited where they worked together. He was the new Adam, she was the new Eve. He was the Redeemer, she was the co-redemptrix. 
Origen, one of the first theologians, noticed something interesting seen at the foot of the cross. When Jesus says woman behold your son, the Greek for your son has the definite article. Now in English, we don't use the definite article with possessive adjectives. So what Origen noticed is a subtle point that we can't express in translation. Ancient Greek uses the definite article to indicate that a noun signifies something that's already known to the reader. So here it means that the son in question is the son, the one already known to the reader as Mary's son. But this, as Origen notes, is Jesus. So when Jesus says woman behold your son, he is saying to his mother that the beloved disciple is Jesus. And this is the point. There at the foot of the cross, the beloved disciple, who is Saint John but represents every disciple, becomes Jesus, which means Mary becomes his mother. 
Every Christian is another Christ, conformed to Christ by baptism. At the foot of the cross, Mary is mystically in labor pains, in the greatest pains, to give birth to Christ in us, so that we no longer live our own life, but Christ will live in us. Therefore she is the mother of every disciple of Christ, the mother of the Church. 
This helps us better understand the scene of Revelation 12. The child is Christ but the labor pains are so that Christ will be born in us, not at Bethlehem. 
After the scene we have mentioned at the foot of the cross, Christ gives a loud cry and gives up the ghost, the Holy Ghost we might say. His suffering is over but Mary's continues. A soldier takes a lance and thrusts it into the side of Christ, all the way to his heart. But in a very real way, the heart he pierces is Mary's. Out of the side of Christ, asleep in death on the cross, comes the Church in the form of blood and water, signs of the sacraments of baptism in the Holy Eucharist. For the Church comes from the side of Christ, asleep in death on the cross. As Eve came from the side of Adam, asleep in paradise, near the Tree of Life, the cross is of course the true Tree of Life. 
Now, I've said that Mary is the new Eve but we shouldn't be surprised if the Church also seems to bear the figure of Eve. For Mary is the mother of the Church and daughters often resemble their mothers. That is why the scene of the woman clothed with the sign in Revelation 12 seems to apply to the Church as well, at least in part.
So, we see how the foot of the cross is a very important place for Mary's motherhood. But it does not end there because the Church needs the Holy Spirit before it can go forth into the world. And that is what happens at Pentecost. After the labor pains, the Church is born and can move about in the world. Mary was the praying heart of the Church at Pentecost and after her Assumption, she continues to intercede for us from heaven. She is our mother by her sufferings and our mother by her prayers. Let us make good use of the graces that cost her so much. 
Praise be Jesus and Mary, now and forever.