Traditionally, Ember days are three days of special prayer and penance offered to God by the Church in thanksgiving for the graces of the previous season and imploring Him for an increase of grace for the new season. They occur four times a year, corresponding to the four natural changes of season. From antiquity, Wednesday, Friday, and Saturday have been observed by Christians as days of fast and penance - Wednesday to compassionate Christ in His betrayal, Friday to honor the death of Christ, and Saturday to join with Our Sorrowful Mother in waiting for the Resurrection. The Ember days are observed the Wednesday, Friday, and Saturday of the third week of Advent, the first week of Lent, the week after Pentecost, and mid-September. Pope St. Leo the Great considered the Ember days to be of Apostolic origin. A few links for further reading about Ember days here, here, and here.
We might think of the Ember days as our quarterly spiritual check-ups, a time to ask ourselves, "How is my spiritual life really doing? Is there something that I should be doing that I am not? Or something that I am doing, but need to renew my effort and intention?" As the spring Ember days fall in Lent, a period already devoted to prayer and penance, we might find it helpful to spend these days reflecting on why we are disciplining ourselves: to enter more fully into union with Christ, our Crucified Savior. In keeping with the tradition of the Church, the sisters observe these days as days of abstinence and special prayer. Prayer for priests (our specialty!) is particularly encouraged because Ember Saturdays were customarily days for the conferral of Holy Orders.
"We adore Thee, O Christ, and we bless Thee
Because by Thy holy cross Thou hast redeemed the world."