From ETWN News:
In 1216, at St. Francis’ request, Pope Honorius III granted a plenary indulgence to those who visit the chapel. Later popes expanded the indulgence to include any basilica, cathedral, or parish church.
An indulgence is the remission of the temporal punishment due to sins that have already been forgiven, and it can be plenary or partial. A plenary indulgence requires that the individual be in the state of grace by the completion of the acts and have complete detachment from sin. The person must also sacramentally confess his or her sins and receive Communion up to about 20 days before or after the indulgenced act. Anyone who visits a Catholic church with the intention of honoring Our Lady of the Angels and recites the Creed, the Our Father, and prays for the pope’s intentions may receive a plenary indulgence on Aug. 2.