Sacrosanctum Concilium

But in order that the liturgy may be able to produce its full effects, it is necessary that the faithful come to it with proper dispositions, that their minds should be attuned to their voices, and that they should cooperate with divine grace lest they receive it in vain [28].

-Second Vatican Council, Constitution on the Sacred Liturgy Sacrosanctum Concilium (4 December 1963), §11, at The Holy See, www.vatican.va.

The importance of disposition. This pertains because sacramentals/blessings are a means by which disposition can be cultivated.

This article is quoted in the preanotanda of the book of blessings.

This article cites Paul 2Cor6:1 "Working together, then, we appeal to you not to receive the grace of God in vain."