Q: The Office for the Liturgical Celebrations of the Supreme Pontiff’s document “The Priest in the Concluding Rites of the Mass” states in section 3 paragraph 1 that, “In the Rites of Conclusion of the Holy Mass the priest is still carrying out a priestly task, namely, of mediation between God and the faithful people. The priest here invokes on the people the divine blessing, while in the name of the people he thanks God for the gifts already received by his kindness. Here also he acts “in persona Christi.” Because of this, he does not say in the plural “may the omnipotent God bless us…” He speaks in the name of the Person of Christ and as minister of the Church, because of this he imparts the blessing, while invoking it, and he sends the faithful to the daily mission of life: “may God bless you” and “Go in peace.” Given that Baptisms which use the formula “We baptize you…” are invalid, does this mean that blessings by the presider at the end of Mass using “May God bless us…” can be considered invalid blessings?
==
A: appreciate your concern to ensure the proper blessing of the faithful. The Congregation for the Doctrine of the Faith has indeed clarified that any change to the baptismal formula renders the sacrament invalid. There has been no such statement regarding a change in the formula of blessing.
When a layperson presides over Morning and Evening Prayer from the Liturgy of the Hours, he or she concludes with the formula, “May the Lord bless us, protect us from all evil and bring us to everlasting life.” Consequently, I’d be hesitant to say that an ordained priest who says at the end of Mass, “May almighty God bless us” is using an invalid formula. I would say, however, that it is not the correct formula, and it deprives the people of the force of his blessing. Similarly, a deacon’s charge is not to dismiss himself with the people, but to dismiss the people. Still, the formula, “Let us go in peace” could hardly be considered invalid.
I concede that questions of validity are canonical, not liturgical, so I am giving uninformed opinions here. The clarification of the baptismal formula came from the Vatican’s congregation that deals with doctrine, not the one that deals with liturgy.