Even a quick look at the monastic life will reveal how important the psalms are to the spiritual life.
In choir, singing the psalms is the major part of the Divine Office. In some monasteries in the Middle Ages the monks would work their way through all 150 psalms in a week. In most places the majority of the psalms are sung through in a month.
Priest and deacons are still required to recite the Divine Office, and when the whole office is said–even in its modern abbreviated form we recite fifteen psalms a day: the Invitatory, three at the Office of Readings, three at Matins, three at Mid Day Prayer and three at Vespers and two at Compline.
Is this just to fill the time? Of course not. The psalms give us words for worship. We want to “pray without ceasing” but we lack the words. We run out of things to say and the psalms are just the words we need.
The psalms are not only the inspired word of God, but they are also the words of men, and they are not only the intellectual thoughts of men or the inspiring ideas of men. They are words of worship, words of prayer, words of supplication, words of anguish–all from the heart. The psalms are therefore important because they are one of the key ways for our faith to make the long journey from the head to the heart.
When we recite or sing the psalms our heart opens to God, and we step past the worries of the world to open not just our minds to the Lord in thought and logic, but also we open our hearts to God who’s sacred heart is always open to us.