7 To this twofold ground of His power and domination He graciously allows us, if we think fit, to add voluntary consecration. Jesus Christ, our God and our Redeemer, is rich in the fullest and perfect possession of all things: we, on the other hand, are so poor and needy that we have nothing of our own to offer Him as a gift. But yet, in His infinite goodness and love, He in no way objects to our giving and consecrating to Him what is already His, as if it were really our own; nay, far from refusing such an offering, He positively desires it and asks for it: "My son, give me thy heart." We are, therefore, able to be pleasing to Him by the good will and the affection of our soul. For by consecrating ourselves to Him we not only declare our open and free acknowledgment and acceptance of His authority over us, but we also testify that if what we offer as a gift were really our own, we would still offer it with our whole heart. We also beg of Him that He would vouchsafe to receive it from us, though clearly His own. Such is the efficacy of the act of which We speak, such is the meaning underlying Our words.
Source: Annum Sacrum (Vatican.va)