145 To this lofty dignity of the Church's prayer, there should correspond earnest devotion in our souls. For when in prayer the voice repeats those hymns written under the inspiration of the Holy Ghost and extols God's infinite perfections, it is necessary that the interior sentiment of our souls should accompany the voice so as to make those sentiments our own in which we are elevated to heaven, adoring and giving due praise and thanks to the Blessed Trinity; "so let us chant in choir that mind and voice may accord together." It is not merely a question of recitation or of singing which, however perfect according to norms of music and the sacred rites, only reaches the ear, but it is especially a question of the ascent of the mind and heart to God so that, united with Christ, we may completely dedicate ourselves and all our actions to Him.
Source: Mediator Dei (Vatican.va)