(א) חזן: בָּרְכוּ אֶת ה' הַמְברָךְ:
(ב) קהל וחזן: בָּרוּךְ ה' הַמְברָךְ לְעולָם וָעֶד:
Bless YHVH who is to be blessed.
Blessed be YHVH who is to be blessed for ever and ever.
(translation by Joel Hoffman as in My People's Prayer Book)
Marc Brettler, My People's Prayer Book (Vol. 1, pg. 30)
How can human beings bless God, who is the source of all blessings, and blesses all created beings, including humanity (Gen. 1:22, 28)? ...In Nehemiah 9:5 [ we read] "The Levites...said, 'Rise and bless Adonai your God for ever and ever...The custom of standing during the Bar'khu has ancient roots; it likely reflects the practice of standing before someone of a higher social status...[The] notice of the eternality of God raises a central theme that is probably no accident that the entire rubric of the Sh'ma and Its Blessings opens with it and closes with it too (end of...G'ullah [Mi Chamocha] by quoting Exodus 15:18 "Adonai will reign for ever and ever."
Elliot Dorff, My People's Prayer Book, (Vol. 1, Pg. 30)
Bar'khu is an invitation to acknowledge God, derived originally, perhaps, from berekh, "knee", since people in antiquity would drop to their knees before a monarch to acknowledge his or her sovereignty.
Elliot Dorff, My People's Prayer Book, (Vol. 1, Pg. 30)
...the root b.r.kh. still means acknowledging God, placed here (at the very beginning of the [Sh'ma section of the service]) to ask us to transcend our self-centered view of the world and our self congratulatory stance within it. The Torah, in fact, defines idolatry as the view that "my strength and the power of my hand accomplished all these things" (Deut. 8:17). By opening prayer with Bar'khu and by repeating it, as Barukh, throught the Siddur's many "blessings," the [prayer service] reenforces the importance of recognizing our creatureliness before our creator. Adopting that appropriately humble attitude prompts us to confront the frightening fact that we are not in full control of our lives...Bar'khu evokes a certain awe, therefore, and even fear. But simultaneously, recognizing our dependence upon God as sovereign moves us to praise and thanksgiving for what we do in fact have.
Lawrence Kushner and Nehemia Polen, Filling Words With Light, pg. 48
But how can a person actually bless God! Through speech, suggests Hayyim of Volozhyn, people can "call forth the divine flow of blessing." We can evoke what would otherwise have remained only latent, unrealized, unfulfilled. We cannot, to be sure, put something there that was not already there, but we can bring something into reality that was only hitherto a possibility. Thus the one who blesses becomes an agent of self-realization and fulfillment for the one who receives the blessing. We "conjure" a blessing. Even for God. And when we "bless" God, since God is the source of all life, we effectively enable the Holy One to bless us. In blessing God, we are blessing ourselves!
The one who offers a blessing is like a coach whispering to an athlete before the competition, "You can do it!" More than encouragement, positive spin, or sincere wish, the words of blessing literally bring forth and make real an otherwise unrealizable force. In this way, blessing is not supplication but symbiosis. God needs us to summon blessings, just as we could not live without them. And so the service begins: Bar'khu et Adonai, "Let us bless God..."