This is the explanation given from the Catholic Encyclopedia
" Since, then, blessings, in the sense in which they are being considered, are entirely of ecclesiastical institution, the Church has the power to determine who shall have the right and duty to confer them. This she has done by entrusting their administration to those who are in sacerdotal orders. The solitary case in which one inferior to a priest is empowered to bless, is where the
deacon blesses the paschal candle in the ceremonies of Holy Saturday. This exception is more apparent than real. For in the instance referred to the
deacon acts by way of a deputy and, moreover, employs the grains of
incense already blessed by the celebrant. Priests, then, are the ordinary ministers of blessings, and this is only in the fitness of things since they are ordained, as the words of the Pontifical run: “ut quæcumque benedixerint benedicantur, et quacumque consecraverint consecrentur” (That what-ever they bless may be blessed, and whatever they consecrate shall be consecrated). When, therefore, laymen and women are represented as blessing others it is to be understood that this is an act of will on their part, a wish or desire for another’s spiritual or temporal prosperity, an appeal to
God which has nothing to recommend if but the merits of personal sanctity. The ordinary greetings and salutations that take places between
Christians and Catholics, leavened by mutual wishes for a share of heavenly grace, must not be confounded with liturgical blessings.
St. Gregory first definitely taught that the
angels are divided into hierarchies or orders, each having its own role to play in the economy of creation. Similarly the Church recognizes different orders or grades among her ministers, assigning to some higher functions than to others. The working out of this idea is seen in the case of conferring blessings. For while it is true that a priest can ordinarily give them, some blessings are reserved to the Supreme Pontiff, some to bishops, and some to parish priests and religious. The first class is not large. The pope reserves to himself the right to bless the
pallium for
archbishops, Agnus-Deis, the
Golden Rose, the Royal Sword, and also to give that benediction of persons to which an
indulgence of some days is attached. He may, and in the case of the last mentioned often does, depute others to give these. To bishops belongs the privilege of blessing abbots at their installation, priests at their ordination, and virgins at their consecration; of blessing churches, cemeteries, oratories, and all articles for use in connection with the altar, such as chalices, vestments, and clothe, military standards, soldiers, arms, and swords; and of imparting all blessings far which Holy Oils are required. Some of these may, on delegation, be performed by inferiors. Of the blessings which priests are generally empowered to grant, some are restricted to those who have external jurisdiction, like rectors or parish priests, and others are the exclusive prerogative of persons belonging to a religious order. There is a rule, too, by which an inferior cannot bless a superior or even exercise the ordinary powers in his presence. The priest, for instance, who says Mass at which a bishop presides is not to give the final blessing without permission from the prelate. For this curious custom authors cite a text from the Epistle to the Hebrews: “And without all contradiction that which is less is blessed by that which is greater” (vii, 7). It would seem an overstraining of the passage to say that it affords an argument for maintaining that an inferior minister cannot bless one who is his superior in rank or dignity, for the text either merely ennunciates an incident of common usage, or means that the inferior by the fact that he blesses is the greater, since he acts as the representative of
God
Taken from…
www.newadvent.org
