Van Slyke

Hence blessing or consecrating a thing in general or
water in particular entailed breaking Satan’s influence
over it, so that it could no longer serve as an instrument
of his hate.54 Then, by the power of Christ entrusted
to the Church, the thing blessed could be used as an
efficacious instrument for good – assuming the proper
disposition of the person who benefits from the use of
the item.

- Daniel G. Van Slyke, "The Order for Blessing Water: Past and Present," Antiphon 8, no.2 (2003), 18.

Van Slyke

One scholar of holy water, writing before Vatican
II, expressed quite a different view of the state of
creation in the following passage: “By the fall of our
first parents, the spirit of evil obtained influence not
only over man, but also over inanimate nature, whence
he is called in Scripture ‘the prince of this world’” (Jn
12:31, 14:30, 16:11). For this reason, when the Church
exorcizes some thing, “the curse put upon it is removed,
and Satan’s power over it either destroyed entirely, or
at least diminished.”

- Daniel G. Van Slyke, "The Order for Blessing Water: Past and Present," Antiphon 8, no.2 (2003), 18.

Van Slyke

(the notion) the “liturgy of the world”
could shed light on the general consensus articulated
by many theologians writing on blessings in the post-
Conciliar period: God’s creatures are blessed from their
creation; liturgical blessings are opportunities to praise
and thank God for this, and, from the pastoral
perspective, to edify those present by recalling it.

- Daniel G. Van Slyke, "The Order for Blessing Water: Past and Present," Antiphon 8, no.2 (2003), 18.

Van Slyke

What theological shifts, it may be asked, led to the new understanding that entailed the wholesale rewriting of the Ritual’s blessings? David Stosur reasons that, in the absence of sustained attention given to blessings in and of themselves, “a contemporary theology of blessings . . . must simply be extrapolated from approaches that theologians since Vatican II have taken to the sacraments and to the liturgy in general.”48 He proceeds to do this, appealing particularly to reflections on the liturgy by Otto Semmelroth, Edward Schillebeeckx, and Karl Rahner.

- Daniel G. Van Slyke, "The Order for Blessing Water: Past and Present," Antiphon 8, no.2 (2003), 18.

Dr.Van Slyke's analysis of the theological shift after the council helps me to understand which aspects of the classical theology of blessing are important.

Rivard

Blessing manifests itself primarily as the power of fertility, both within the family and in the practice of farming, and as such represents a sharing in the life of God and the power to pass on that life by virtue of the blessing of creation.

- Derek A. Rivard, Blessing the World: Ritual and Lay Piety in Medieval Religion. (Washington, D.C: Catholic University Press, 2009), 27.

This definition of blessing comes from the historical-critical viewpoint. From a theological point of view the historical-critical is limited because it doesn't regard the Church as it is, instituted by Christ as the means for salvation of all mankind. Rather it views the Church as a historical accident... (that's strong but that's what this kidn of definition ignores is the spiritual authority of the Church.)

Paschang

That the power of constituting Sacramentals, which the Church claims in canon 1145 is reasonable and legitimate, is a matter that can hardly be called into question. It is a power which Christ conferred upon her in the plainest terms. He gave the Apostles and the Church the power over unclean spirits:"heal the sick, raise the dead, cleanse the lepers, cast out devils, freely have you received, frely give."

- John L. Paschang, Sacramentals According to the Code of Canon Law. (Washington,D.C.: Catholic University of America, 1925), 19.

Paschang gives great reference to scripture to ground his presentation of the theology of sacramentals.

He also makes a reference to Pohle-Pruess which is good (The Sacraments p.115-116) where they give an excellent image of the Church providing for the good of her children.

Aertnys - Theologia Moralis

Verumtamen Ecclesiae orationes apud Deum magnam vim habent ad impetrandum; diligit enim eam tamquam sponsam.

Never the less, the prayers of the Church have great power with God of obtaining favor, whom he loves as his spouse.

- Aertnys, Josef and Damen, C. A. Theologia Moralis: Secundum Doctrinam Sancti Alfonsi de Ligorio Doctor Ecclesiae, vol. 2. (Marietti, 1950), 35.

The special efficacy of the prayer of the Church is the basis of the power of sacramentals and therefore blessings. Here, Aertnys cites Thomas (n. 90-93 S. Thom. 3. qu. 87. a. 3.)

It will be necessary to establish the efficacy of the prayer of the church to be able to speak of the nature of blessings.

Sacrosanctum Concilium

Rightly, then, the liturgy is considered as an exercise of the priestly office of Jesus Christ. In the liturgy the sanctification of the man is signified by signs perceptible to the senses, and is effected in a way which corresponds with each of these signs;

- Second Vatican Council, Constitution on the Sacred Liturgy Sacrosanctum Concilium (4 December 1963), §7, at The Holy See, www.vatican.va.

In quote from section 7 of SC we see reflected the sacramental character of the liturgy itself. I take this to be a reflection of the Canons from Trent session 22 cited earlier, though I need to demonstrate why I think that.

This pertains to sacramentals because like the liturgy they are instituted by the church to dispose men to and to actually impart the fruits of Christ's sacrifice. Or as it says earlier in section 7, to sanctify men and give glory to God.

Code of Canon Law

Can. 1167 §1 Only the Apostolic See can establish new sacramentals, or authentically interpret, suppress or change existing ones. §2 The rites and the formulae approved by ecclesiastical authority are to be accurately observed when celebrating or administering sacramentals.

Code of Canon Law, c.1167, §1-2, in Code of Canon Law: Latin-English Edition (Washington, DC: Canon Law Society of America, 1999), 423.

I think this canon is very closely related to canons of Trent (Council of Trent. Session 22 (17 Semptember 1562)) which defend the Church's special relationship to Christ's sacrifice.

Code of Canon Law

Sacramentalia sunt signa sacra, quibus, ad aliquam sacramentorum imitationem, effectus praesertim spirituales signifcantur et ex Ecclasiae impretratione obtinentur. - The Sacramentals are objects or actions resembling the Sacraments which the Church makes use of by way of intercession to obtain especially spiritual effect.(Augustine's translation).

- Code of Canon Law, c. 1166, in Code of Canon Law: Latin-English Edition (Washington, DC: Canon Law Society of America, 1999), 423.

This Canon on the sacramentals is significant because it provides a scientific definition. This canon slightly more precise than the pertinent canon in the 1917 code.

This and subsequent canons can be linked to canons of Trent, defending the spiritual and temporal authority of the Church in establishing rites. I think this can be developed into an ecclesiological rationale / defense / understanding of the nature and efficacy of blessings.