What is the reason for saying the Yehi Ratzon for Tehillim?

The Yehi Ratzon before Tehillim is said as a personal prayer and request that the Psalms about to be recited be accepted and considered as if King David were saying them himself. Although the words are being said in a context different than when they were originally composed, we beseech that the words, vowels, pronunciations, and tunes should stand in their own merit.