Thomas Aquinas

“ It seems that there is not in the sacraments a power of causing grace. For the power of causing grace is a spiritual power. But a spiritual power cannot be in a body; neither as proper to it, because power flows from a thing's essence and consequently cannot transcend it ”

“ But there is nothing to hinder an instrumental spiritual power from being in a body; in so far as a body can be moved by a particular spiritual substance so as to produce a particular spiritual effect; thus in the very voice which is perceived by the senses there is a certain spiritual power, inasmuch as it proceeds from a mental concept, of arousing the mind of the hearer. It is in this way that a spiritual power is in the sacraments, inasmuch as they are ordained by God unto the production of a spiritual effect. ”

“ Consequently, by faith Christ's power is united to us. Now the power of blotting out sin belongs in a special way to His Passion. And therefore men are delivered from sin especially by faith in His Passion, according to Rom. 3:25: "Whom God hath proposed to be a propitiation through faith in His Blood." Therefore the power of the sacraments which is ordained unto the remission of sins is derived principally from faith in Christ's Passion.
Reply to Objection 3: Justification is ascribed to the Resurrection by reason of the term "whither," which is newness of life through grace. ”

“ Just as the one same power of the principal agent is instrumentally in all the instruments that are ordained unto the production of an effect, forasmuch as they are one as being so ordained: so also the one same sacramental power is in both words and things, forasmuch as words and things combine to form one sacrament. ”

“ In like manner the corporeal sacraments by their operation, which they exercise on the body that they touch, accomplish through the Divine institution an instrumental operation on the soul; for example, the water of baptism, in respect of its proper power, cleanses the body, and thereby, inasmuch as it is the instrument of the Divine power, cleanses the soul: since from soul and body one thing is made. ”

“ It does indeed, and penetrates every secret hiding-place of the conscience. For subtle and clear as it is, the blessing of Christ makes it yet more subtle, so that it permeates into the very principles of life and searches the inner-most recesses of the heart. ”

“ Further, the power of the sacraments seems to depend on faith. for as Augustine says (Tract. lxxx in Joan.) , the Divine Word perfects the sacrament "not because it is spoken, but because it is believed." ”