As Catholics, we acknowledge Purgatory, a temporary state where those that die with venial sin may be cleansed/purified before entering Heaven. Those in purgatory, however, may be helped by our prayers. I don't want to explain the whole doctrine now though, so please see the link for more information.
I just wanted to remind everyone what I learned only a few weeks ago, that the Blessed Virgin Mary helps release more souls from Purgatory on Christmas Day than on any other day. Remember, Christ saves us, but His Mother Mary, who was assumed into Heaven, helps by bringing these souls to Our Lord in Heaven through her prayers. Please say a prayer for the souls in purgatory especially today.
There are more souls released from Purgatory during the Consecration of the Mass than at any other time. Christmas is the day of the year when most souls are delivered; followed by feast days of Our Lord, Our Lady, and great saints. Souls receive much grace from prayers offered for them on their birthdays, day of baptism, and anniversary of death. The more we work for the poor souls now the more others will pray for us, the more merciful will Christ be with us when we’re in Purgatory.
Our Lady asked that we pray very much for the poor souls; she asked that we pray:
5 Apostle's Creed
1 Hail Holy Queen
1 Our Father
1 Glory Be
Our Lady said that if we pray the prayers "we’ll deliver so many souls, so many souls. The Holy wounds are the treasure of treasurers for the souls in Purgatory." As Scripture states, "It is a holy and wholesome thought to pray for the dead that they may be loosed from their sins" (2 Mac 12:46)
In an approved apparition by the Church, Our Savior, Jesus Christ, gave St. Gertrude the Great this prayer. She said that 1,000 souls would be released every time it is said:
Eternal Father, I offer Thee the most Precious Blood of Thy Divine Son, Jesus Christ, in union with the Masses said throughout the world today, for all the Holy Souls in Purgatory, for sinners everywhere, for sinners in the Universal Church, for those in my own home and within my family. Amen.
Note: The above image of Holy Mass is of a Tridentine Catholic Mass for Christmas Mass at Midnight.