Mark 11:24
Amen I say to you, whatsoever you ask when you pray, believe that you shall receive, and it shall be done to you.
Denzinger
2276: The Divine Office, the Public Prayer of the Church
The Divine Office, the Public Prayer of the Church [From the Encyclical, "Ad catholic) sacerdotii," December 20, 1935]
Finally, the priest in this matter, also, performing the work of Jesus Christ, who “passed the whole night in the prayer of God” [Luke 6:12], and “always lived to make intercession for us” [Heb. 7:25], is by office the intercessor with God for all; it is among his mandates to offer not only the proper and true sacrifice of the altar in the name of the Church to the heavenly Godhead, but also “the sacrifice of praise” [Ps. 49:14] and common prayers; he, indeed, by the psalms, the supplications, and the canticles, which are borrowed in great measure from Sacred Scripture, daily, again and again discharges the duty of adoration due to God, and he performs the necessary office of such an accomplishment for men…
If private supplication is so powerful because of the solemn and great promises given by Jesus Christ [Matt. 7:7-11; Mark 11:23; Luke 11:9-13], then the prayers, which are uttered in the Office in the name of the Church, the beloved spouse of the Redeemer, without doubt enjoy greater force and virtue.