Pope Francis has granted a "plenary indulgence" for those taking part.
In Catholic doctrine an indulgence frees you from being punished for your previously committed sins or it can be passed on to dead relatives to shorten their time in purgatory.
Even those following events on TV and radio can achieve a partial indulgence as long as they recite the Our Father, the Creed and other devout prayers.
Martin Luther's opposition to the sale of indulgences was one of the main causes of the Protestant Reformation in the 16th Century.
The Sacred Apostolic Penitentiary, the Vatican body dealing with forgiveness of sins, said pilgrims would have to attend confession and Mass, pray for the Pope's intentions and participate in some function during the five-day event. BBC.
What are Indulgences?
Indulgence a grant by the Pope of remission of the temporal punishment in purgatory still due for sins after absolution.
In order to believe in indulgences, one must also believe in purgatory. To receive an “indulgence” from the Catholic Church is their belief that certain works-based blessing from a priest can earn someone bonus points to get out of purgatory and into heaven.
To make this deceptive doctrine work, the Catholic Church tied it closely to the false doctrine of purgatory.
In Roman Catholic theology, purgatory (Latin: Purgatorium, via Anglo-Norman and Old French) is an intermediate state after physical death in which some of those ultimately destined for heaven must first "undergo purification, so as to achieve the holiness necessary to enter the joy of heaven," holding that "certain offenses can be forgiven in this age, but certain others in the age to come." And that entrance into Heaven requires the "remission before God of the temporal punishment due to sins whose guilt has already been forgiven," for which indulgences may be given which remove "either part or all of the temporal punishment due to sin," such as an "unhealthy attachment" to sin.