An individual may ask to have a priest offer a Mass for several reasons: for example, in thanksgiving, for the intentions of another person (such as on a birthday), or, as is most common, for the repose of the soul of someone who has died. One must never forget the infinite graces that flow from the Sacrifice of the Mass which benefit ones soul. Pope Leo XIII in his encyclical "Mirae caritatis" (1902) beautifully elaborated this point and emphasized the connection between the communion of saints with the Mass: "The grace of mutual love among the living, strengthened and increased by the sacrament of the Eucharist, flows, especially by virtue of the Sacrifice [of the Mass], to all who belong to the communion of saints. For the communion of saints is simply ... the mutual sharing of help, atonement, prayers and benefits among the faithful, those already in the heavenly fatherland, those consigned to the purifying fire, and those still making their pilgrim way here on earth."
We find not only the origins of this practice dating to the early Church but we also clearly recognize its importance. When we face the death of someone, even a person who is not Catholic, to have a Mass offered for the repose of his soul and to offer our prayers are more beneficial and comforting than any other sympathy card or bouquet of flowers. To have a Mass offered on the occasion of a birthday, anniversary or special need is appropriate, beneficial and appreciated. Catholic Education Resource Center