"Since the year 1300 when Pope Boniface VIII declared the first Holy Year, the Catholic Church has regularly celebrated “Holy Years,” usually every twenty-five years (at least since 1470), except for special circumstances, like in 1983 when a Holy Year was declared to mark the 1950th anniversary of the death and resurrection of our Lord. A major aspect of the Holy Year has been that of pilgrimage to Rome to make reparation for sin and to renew the conversion of one’s life.
A very important symbolic act performed by each pilgrim has been to pass through the Holy Door. Christ identified Himself as “the door.” In his bull Incarnationis Mysterium proclaiming this Holy Year, Pope John Paul II stated that the Holy Door “…evokes the passage from sin to grace which every Christian is called to accomplish. Jesus said, ‘I am the door’ (John 10:7) in order to make it clear that no one can come to the Father except through Him. This designation which Jesus applies to Himself testifies to the fact that He alone is the Savior sent by the Father. There is only one way that opens wide the entrance into this life of communion with God: This is Jesus, the one and absolute way to salvation. To Him alone can the words of the psalmist be applied in full truth: ‘This is the door of the Lord where the just may enter’ (Psalm 118:20).”
Therefore to pass through the door from the outside of St. Peter’s into the basilica is to pass from this world into the presence of God, just as in the old Temple of Jerusalem, the High Priest on the Feast of Yom Kippur passed through the veil covering the doorway of the Holy of Holies to enter into the presence of God to offer the sacrifice of atonement. Moreover, to pass through the door is to confess with firm conviction that Jesus Christ is the Son of God, the Lord, and the Savior who suffered, died, and rose for our salvation. With great courage, a person freely decides to cross the threshold leaving behind the kingdom of this world so as to enter the new life of grace of the Kingdom of God.
In opening the door, the Holy Father has traditionally struck the door three times with a silver hammer. The striking of the door also has symbolic meaning: Moses struck the rock so that water would pour out miraculously to quench the thirst of the people (Numbers 20:6ff); the Holy Year is a time when God pours forth abundant graces to quench the thirst of our souls. God struck the earth to free St. Paul and Silas from prison, which resulted in the jailer and his family asking for baptism (Acts 16:25ff); God has struck our hearts opening them to His graces, beginning with the saving grace of Baptism. As our Lord hung upon the cross, the soldier struck His most Sacred Heart, and out flowed blood and water, symbols of the Holy Eucharist and Baptism (John 19:31f) which nourish each of our souls. In all, the striking of the door symbolizes the release of graces, flowing abundantly to the faithful." - MORE BELOW LINK
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