24 But the chief element of divine worship must be interior. For we must always live in Christ and give ourselves to Him completely, so that in Him, with Him and through Him the heavenly Father may be duly glorified. The sacred liturgy requires, however, that both of these elements be intimately linked with each another. This recommendation the liturgy itself is careful to repeat, as often as it prescribes an exterior act of worship. Thus we are urged, when there is question of fasting, for example, "to give interior effect to our outward observance." Otherwise religion clearly amounts to mere formalism, without meaning and without content. You recall, Venerable Brethren, how the divine Master expels from the sacred temple, as unworthily to worship there, people who pretend to honor God with nothing but neat and wellturned phrases, like actors in a theater, and think themselves perfectly capable of working out their eternal salvation without plucking their inveterate vices from their hearts. It is, therefore, the keen desire of the Church that all of the faithful kneel at the feet of the Redeemer to tell Him how much they venerate and love Him. She wants them present in crowds - like the children whose joyous cries accompanied His entry into Jerusalem - to sing their hymns and chant their song of praise and thanksgiving to Him who is King of Kings and Source of every blessing. She would have them move their lips in prayer, sometimes in petition, sometimes in joy and gratitude, and in this way experience His merciful aid and power like the apostles at the lakeside of Tiberias, or abandon themselves totally, like Peter on Mount Tabor, to mystic union with the eternal God in contemplation.
Source: Mediator Dei (Vatican.va)