Mother's Day has its roots in ancient Greece and Rome as so many of our holidays do. Pagan societies celebrated their maternal goddesses during the spring as the buds swelled with new life. Holy Mother Church, knowing that you can't replace something with nothing, tended throughout history to sacramentalize the natural by replacing pagan feasts with holy days. So the date for Christmas was chosen to replace the winter solstice celebrations with welcoming the birth of Christ. In the 13th century the Church did the same thing with the month of May when they named it Mary's month. Their is something particularly appropriate about honoring our natural mothers during the month dedicated to our Blessed Mother.
In the U.S. the celebration of Mother's Day is attributed to Anna Jarvis who wished to honor her own mother's desire that there be a particular day recognizing the work and contributions of mothers. Anna Jarvis herself never married or had children of her own, but was instrumental in the effort that led in 1914 to President Woodrow Wilson signing a Joint Resolution that made the second Sunday in May Mother's Day.
Joszef Cardinal Mindszenty on Motherhood
The most important person on earth is a mother. She cannot claim the honor of having built Notre Dame Cathedral. She need not. She has built something more magnificent than any cathedral--a dwelling for an immortal soul, the tiny perfection of her baby's body . . . The angels have not been blessed with such a grace. They cannot share in God's creative miracle to bring new saints to Heaven. Only a human mother can. Mothers are closer to God the Creator than any other creature; God joins forces with mothers in performing this act of creation . . . What on God's good earth is more glorious than this; to be a mother?
Don't forget to say thank you to Mom tomorrow and, even more importantly, offer some prayers that our heavenly Mother will intercede for her.
For more on Mary's month and Mother's Day:
Month of Mary
Mothers Day History and lots more
Catholic books on motherhood