A simple declarative sentence can convey important information. For example, "Matt Klein can sing" tells us a plain fact about Matt. Depending on tone and emphasis, even more information can be conveyed about Matt's abilities. But adding the word "you" to the sentence adds a different dimension.
"Matt Klein, you can sing" is unquestionably directed at the subject of the sentence. The addition of the simple pronoun "you" changes our declarative sentence from its function of imparting information. "You" calls us into relationship with Matt.
There was a time early in the history of Jewish prayer when the word "atah" (which means "you") was not necessarily in the brakha. Even without knowing the meanings of all the words, you can hear the difference already between a statement made ABOUT God and a statement made TO God. That small word, "you," calls us into relationship.
You can skip this next paragraph and not lose the thrust of this lesson:
It is interesting to me that the direct object marker in Hebrew is part of this word. "Et," which has no meaning at all in English, is the word that precedes a proper noun or a definite article ("ha-") after a verb. It puts the subject of the sentence into a direct relationship with the object. "Et," with a slight difference in the vocalization (vowel) is "at," which is the feminine form of the masculine "atah." The first two words of any brakha are "barukh atah." The first two words of evening and morning worship are "barkhu et."
If you want more explanation of what sounds a little like Martin Buber, his books are readily available. However, I am not an existentialist like he was. The "atah" in the brakha is a reminder that when we pray, we are not speaking into the ether, nor are we merely reflecting on the nature of things, nor are we just searching the recesses of our hearts. Prayer is not impersonal.