In a vision at the Chapel of Our Lady of the Angels, the Lord, accompanied by the Blessed Virgin, instructed St. Francis of Assisi to ask whatever favor he desired. St. Francis asked for what came to be known as the Porziuncula Indulgence, otherwise known as the Great Pardon of Assisi. He asked that those who would devoutly visit the Chapel would be forgiven all of their sins and the punishment due them. (This remarkable pardon is similar to the 20th century feast of Divine Mercy.).
At one time, the Pardon was reserved for those who would visit the Chapel on the afternoon of the 1st and all day on the 2nd of August, the 2nd being the feast of Our Lady of the Angels. Over the centuries, the Popes have extended the favor to include every parish Church, beginning at noon of the 1st and ending at midnight of the 2nd of August. (This type of plenary indulgence is known as toties quoties.)
To obtain the plenary indulgence, a person must visit the Chapel of Our Lady of the Angels at Assisi, a Franciscan sanctuary, or one's parish Church, with the intention of honoring Our Lady of the Angels. (At the Chapel in Assisi, the indulgence may be gained on any day throughout the year.)
One must be free of any attachment to venial and mortal sin, and truly repentant. Therefore, it is necessary to make Sacramental Confession, preferably 8 days before or after the visit. It is also necessary to assist at Mass and receive Holy Communion 8 days before or after the feast, although communicating on the feast is customary. It is also required that a person recite the Creed and pray the Our Father, for the intentions of the Holy Father.