The Function of the Baptismal Priesthood at Mass
There are two ways that Christ's priesthood is exercised in the Church. One is the ministerial priesthood, whereby men are ordained as priests to offer the Eucharist, the Most Holy Sacrifice of the Altar. The other is the common priesthood, whereby every baptized Christian is called to offer spiritual sacrifices to God, ultimately offering Him their very selves.
The line between these two priesthoods, which "differ from one another in essence and not only in degree" (Vatican II, Lumen Gentium 10), has been blurred or even erased in the minds of some Catholics today. Some denigrate the ministerial priesthood (or elevate the baptismal priesthood) to equate the two priesthoods, treating the ministerial priest as a mere representative of the congregation, instead of as the representative of Christ. This is utterly opposed by Church teaching, as the documents of Vatican II make clear.
There is a serious lack of understanding concerning the baptismal priesthood and what it truly entails, especially in the context of the Mass. What must be understood is that the baptismal priesthood is an exercise of the apostolate of the laity, just as the ministerial priesthood is an exercise of the apostolate of the ordained. Of course, one must know, then, what the apostolate of the laity is! It just so happens that there is a Vatican II document specifically about that, Apostolicam Actuositatem. In addition to that document, the Dogmatic Constitution on the Church, Lumen Gentium, summarizes the lay apostolate in Part IV (paragraphs 30-38):
[T]he laity, by their very vocation, seek the kingdom of God by engaging in temporal affairs and by ordering them according to the plan of God. They live in the world, that is, in each and in all of the secular professions and occupations. They live in the ordinary circumstances of family and social life, from which the very web of their existence is woven. They are called there by God that by exercising their proper function and led by the spirit of the Gospel they may work for the sanctification of the world from within as a leaven. In this way they may make Christ known to others, especially by the testimony of a life resplendent in faith, hope and charity. Therefore, since they are tightly bound up in all types of temporal affairs it is their special task to order and to throw light upon these affairs in such a way that they may come into being and then continually increase according to Christ to the praise of the Creator and the Redeemer. (Lumen Gentium 31)The word apostolate can be understood as "mission." What is the "mission" of the laity? We are called to live outside the walls of churches and monasteries and convents. We are called to bring the sanctifying presence of Christ into the world: that is why Mass ends with a dismissal, a missio, a mission. In our capacity as baptismal priests, we are called to make of the world (and our lives in it) an offering, a spiritual sacrifice to God, joined to the ministerial priest's sacrifice of the Eucharist.
Some people think (because they were taught so) that Vatican II opened the door to myriad liturgical activities performed by the laity; that's how they interpret the call to "active participation" (Sacrosanctum Concilium 14). That is simply not the case. In all the Council documents, there is but one sentence which speaks directly to the carrying out of liturgical functions by the laity: "Finally, the hierarchy entrusts to the laity certain functions which are more closely connected with pastoral duties, such as the teaching of Christian doctrine, certain liturgical actions, and the care of souls." (Vatican II, Apostolicam Actuositatem 24) While the extraordinary assistance of some laymen at Mass is appreciated in times of necessity, the exercise of the baptismal priesthood at Mass is not rooted in "a visible liturgical rite" (Pope Pius XII, Mediator Dei 93) but rather in the spiritual union of their own sacrifices with the bread and wine presented to the priest, culminating in the union of themselves to the Eucharist offered to the Father.
Part II of this essay will examine the uniting of spiritual sacrifices with the bread and wine in the Offertory.