Encyclical letter of Pope Leo XIII on the Holy Eucharist (May 23, 1902). It is one of the principal modern sources of the Church's doctrine on the Blessed Sacrament, along with Mediator Dei of Pope Pius XII and Mysterium Fidei of Pope Paul VI. Its theme is mainly the marvelous effects of devotion to the Holy Eucharist in the moral and spiritual life of the faithful. The main reason for the troubles in our day, according to Mirae Caritatis, is the lack of charity among people because of their weakening in the love of God. On both counts, the Sacrament of the Eucharist is the most effective way to grow in selfless love.