30 What more suitable occasion can We indicate, Venerable Brethren, for such a union of prayer and reparation, than the approaching Feast of the Sacred Heart of Jesus? The proper spirit of this solemnity, as we amply showed four years ago in Our Encyclical Letter Miserentissimus , is the spirit of loving reparation, and therefore it was Our will that on that day every year in perpetuity there should be made in all the churches of the world a public act of reparation for all the offenses that wound that divine Heart.
Source: Caritate Christi Compulsi (Vatican.va)