Go down and read the thread on the Liturgy of the Hours, particularly the comment by Dominican Brother James Dominic Brent:

When I first started, I ran into the problem that the Psalmist’s mood or prayer often clashed with mine. When I was in a mood for lamentation, the Psalmist was shouting for joy; when the Psalmist was lamenting, I was ready to give praise and thanksgiving to God. Only rarely did the Psalm that was put before me match my mood or state of mind at the moment. How could I persevere in this practice given the routine clash between my prayer mood and the prayer required of me by the Liturgy of the Hours?

I resolved this question by discovering in the Tradition an extremely profound notion that opened up a whole new level of meaning in the Psalms. I discovered St. Augustine’s notion of “the whole Christ”. The whole Christ is the body of Christ both Head and members together. The whole Christ is the single organism composed of both Jesus in himself and all those incorporated into Him by baptism (living and dead). The whole Christ is a quasi-person who speaks and acts like anyone else. According to St. Augustine, it is the whole Christ who prays the Psalms. The Psalter, therefore, is first and foremost the prayer that Jesus prays to the Father. Every line in it is “vox Christi”. Thanks to the Holy Spirit who unites us all as members into Jesus, we have access to the voice or words by which Jesus himself prays to the Father (see Eph.2: 11-18). That is what one prays in the Psalms (see CCC 2599 – 2606, especially 2606).