Vocal prayer is an essential element of the Christian life. To his disciples, drawn by their Master's silent prayer, Jesus teaches a vocal prayer, the Our Father. He not only prayed aloud the liturgical prayers of the synagogue but, as the Gospels show, he raised his voice to express his personal prayer, from exultant blessing of the Father to the agony of Gesthemani.
Source: Catechism of the Catholic Church (Vatican.va)