The simple answer to this question is, “No, a priest does not have to offer Mass each day.” However, such a simple answer would be misleading since a priest, who is ordained to offer the Holy Sacrifice of the Mass, ought to do so each day.
The Code of Canon Law (#276) in the section entitled “The Obligations and Rights of Clerics” states the following: “In leading their lives, clerics are especially bound to pursue holiness because they are consecrated to God by a new title in the reception of orders as dispensers of God’s mysteries in the service of His people. In order for them to pursue this perfection, …they are to nourish their spiritual life from the two-fold table of Sacred Scripture and the Eucharist; priests are therefore earnestly invited to offer the sacrifice of the Eucharist daily….”
A priest generally fulfills this invitation by celebrating the Mass individually or concelebrating with other priests with the faithful present. However, even if a priest is alone, even without the aid of a server, he may still offer the Mass: In his “Holy Thursday Letter” addressed to all of the priests of the Church in 1999, Pope John Paul II taught, “In the Eucharist, the priest personally draws near to the inexhaustible mystery of Christ and of His prayer to the Father. He can immerse himself daily in the mystery of redemption and grace by celebrating Holy Mass, which retains its meaning and value even when, for a just reason, it is offered without the participation of the faithful, yet always for the faithful and for the whole world” (#6). There are numerous stories of priests imprisoned and isolated in Nazi and Communist prison camps who found strength, comfort, and renewed identity in offering by themselves– alone but united with their Savior and the Church– the Holy Mass.
The priest ought to accept the invitation to offer the Holy Mass each day because of who he is. As a minister of word and sacrament and as one who acts in the person of Christ, the identity of the priest becomes most clear in the offering of the Mass, the source and summit of our Catholic spiritual life. The Mass is a memorial, but in the biblical sense, in that it makes present the event itself. Therefore, the Mass entails both memory and presence. Through the Mass, one not only recalls the saving event of the Last Supper, the passion, death, and resurrection, one enters into the ever-present, ever-living reality of that saving event. For the priest, he enters into the very mystery of his priesthood.
When the priest offers the Mass, he invokes and calls down in the epiclesis the Holy Spirit who makes present anew the saving event on the altar. Here the priest extends his hands over the bread and wine and says, “Let your Spirit come upon these gifts to make them holy, so that they may become for us the Body and Blood of our Lord Jesus Christ.” Pope John Paul II taught, “The priest truly acts in persona Christi. What Christ accomplished on the altar of the cross and what earlier still He had instituted as a sacrament in the Upper Room, the priest now renews by the power of the Holy Spirit. At this moment the priest is as it were embraced by the power of the Holy Spirit, and the words which he utters have the same efficacy as those spoken by Christ at the Last Supper” (Gift and Mystery, p. 77). When the priest pronounces the words of consecration, the bread and wine become truly, really, and substantially Christ’s own body and blood, and they represent in a sacramental, unbloody manner the bloody propitiatory sacrifice offered by Him on the cross to His Father for the salvation of the world.
Note that for the most part, the Eucharistic prayers are said in the first person plural– asking for God’s forgiveness, praising and thanking God, and imploring God’s blessing. When the priest comes to the words of consecration– Jesus’s own words– he pronounces them in the first person singular, and shifts from the past tense and into the present tense. If the priest kept the past tense and some sort of indirect discourse, he would simply be remembering what Jesus did rather than what Jesus is doing. Christ, therefore, is the principle actor, and the priest speaks and acts in the person of Christ to make His sacrifice present in a new way.
The priest acting in the person of Christ is thus a minister of the Word of God, a minister of Sacraments, and a steward of the mystery of faith. When we reflect on the office of priest acting in persona Christi, we as a Church step back with a reverential awe. However, any priest must tremble.
Therefore, while the priest is not officially obligated to offer the Holy Sacrifice of the Mass each day and Canon Law simply “invites” him to do so, the priest ought to want to offer the Mass for in so doing he finds his identity, purpose, and strength as priest.