Ambrose of Milan called the Psalter a gymnasium for the soul. John Calvin called it a mirror. John Goldingay called it 150 things we know we can say to God.
It's more complicated (I sang Psalms every Sunday in my childhood, for example) but let's say I fell in love with the Psalms in the earlier half of the 1990s, because of Eugene Peterson's book Working the Angles . I had been having difficulty praying - difficulty with wanting to pray - and Peterson showed me the way of the Psalms, which resolved my difficulties. Maybe a decade later my favourite bookseller, Byron Burger, recommended Jim Cotter's Out of the Silence (a prayerbook that includes improvisations on all 150 psalms) that has subsequently ensured that my daily rhythm of praying these poems never become mere rote.