When a priest celebrates Mass each day, he offers each celebration of the Eucharist for a particular person, or intention. By doing so he applies special graces from God upon that person or intention
Similar to how we are able to intercede for others by our personal prayers, the Church is able to intercede for us through the celebration of the Mass. However, since the Eucharist is the “source and summit of the Christian life” the Mass possess a power that our personal prayers do not.
The practice of offering Mass for particular intentions is an ancient one, dating back to the early Church.
Fr. William Saunders explains, “Inscriptions discovered on tombs in Roman catacombs of the second century [give] evidence [for] this practice: for example, the epitaph on the tomb of Abercius (d. 180), Bishop of Hieropolis in Phrygia, begs for prayers for the repose of his soul. Tertullian (c. 200) attested to observing the anniversary of a spouse with prayers and sacrifices, i.e. the Mass.”