A formal call to worship.
Reprinted with permission from The JPS Guide to Jewish Traditions, published by the Jewish Publication Society.
Barkhu (Let us praise) is the ceremonial call to worship by the prayer leader at the formal beginning of the daily morning and evening services. The morning service in the synagogue initially consisted only of the Shema (and its blessings) and the Amidah.
Each worshiper recited the preliminary sections privately at home or in the synagogue before the beginning of the service, which formally began with the Barkhu. Barkhu is not included in the afternoon service, since the Shema is not recited.
After the prayer leader recites the invocation "Barkhu et Adonai hamevorakh" (Praise the Lord, who is [to be] praised), the congregation responds "Baruch Adonai ha-mevorakh l'olam va-ed" (Praised is the Lord, who is [to be] praised for ever and ever). Having summoned the congregation to praise God, the prayer leader repeats the response to indicate that this obligation is equally incumbent on him (or her).
Although literally meaning "bless," in context the word "barkhu" is the equivalent of "praise," for it would be the height of presumption to think that mere mortals could somehow confer anything on God. Instead the Barkhu recognizes that God is the source of all blessings and is an assertion of the worshiper's dedication to fulfill God's will by performing the divine commandments.
Barkhu is recited while standing and only in the presence of a minyan. The prayer leader bows at the word "praise" and straightens at "Lord," while both the prayer leader and the congregation bow at the word "praised" and straighten at "Lord" in the response. The recitation of Barkhu and the practice of standing during it may have originated at the time of Ezra, based on the verse in Nehemiah (9:5), "Rise, bless the Lord your God who is from eternity to eternity: 'May Your glorious name be blessed, exalted though it is above every blessing and praise!'"