However, the custom of requesting a priest to offer the Mass for a specific intention, even when one cannot be physically present at the Mass, is a longstanding tradition in the Church.
This is because the Church considers the Mass as the greatest possible prayer of intercession insofar as it is the perfect offering of Christ to the Father by making present the paschal mystery of his death and resurrection.
Because of the particular role of the priest as mediator between God and man, acting “in persona Christi” when offering the holy sacrifice of the Mass, it is usually considered that special graces may be obtained when he applies the Mass to a particular intention.
The faithful generally make an offering, called a stipend, to the priest in order to apply the Mass to a specific intention. By making this offering, the faithful, by parting with something that is their own, associate themselves more intimately with Christ who offers himself in the sacred Host, and obtain thereby more abundant fruits (See Pope Paul VI’s letter “Firma in Traditione” of June 13, 1974).
This sacrifice has an infinite value and indeed there is no objective limitation to the number of intentions that can be offered at any Mass.
The offering of a stipend is also a means whereby Catholic may contribute to the upkeep of the clergy, and the Church in general.
However, so as to avoid even the appearance of commerce in sacred things, the Church regulates the practice of offering and receiving stipends in canons 945-958 of the Code of Canon Law and in some later decrees on specific applications of the code.
Thus, in normal circumstances, a priest may only accept one stipend for any one Mass even though he may offer up the Mass for several intentions.
Likewise, if he celebrates more than one Mass a day he may keep only one stipend for his personal use and must apply the others to some charitable cause determined by the bishop, often to help support the seminary.
When a Mass cannot be celebrated in the place it was requested, the excess intentions are passed on to other priests or the local bishop. They must assure that all Mass requests are fulfilled within the space of one year.
Some places, dioceses, sanctuaries, etc., that receive more requests than can be celebrated within a year, often entrust these intentions and their stipends to other priests who may not have regular intentions, such as monks and retired priests.
In some cases the extra intentions are also sent to the Holy See, which distributes them throughout the world.