Unlike the weekday Amidah (’standing prayer’) that contains nineteen blessings, the Sabbath Amidah only has seven blessings. Why seven? The Talmud (Berachot 29a) explains that these seven blessings correspond to the seven times the phrase “God’s voice” appears in Psalm 29.
Why did the Sages associate this psalm, which contains not a single mention of Shabbat, to the Sabbath prayers? Also, why did they describe this psalm as the one that David composed “upon the waters"? Why the emphasis on water?
The world appears most advanced and perfected when seen in its developed, built-up state. But upon deeper reflection, it is possible to recognize that there is also a need for destructive forces in the world. If we can perceive the benefits of destructive phenomena — like the positive role played by forest fires in the growth and regeneration of a forest — then we may grasp how also these forces indicate the underlying purpose and Divine wisdom governing the universe.
Water is a particularly apt metaphor for nature’s destructive forces. Water, the seas and the oceans, are the antithesis of human progress and civilization. David composed Psalm 29 while reflecting “upon the water.” He contemplated the great destructive forces in the world — leaving mighty cedars shattered, deserts shaking, and forests stripped bare — and in their deafening roar of upheaval he was able to hear the voice of God. Thus the phrase “God’s voice” is the psalm’s leitmotif, repeated seven times.
This insight is most clearly revealed in the spectacular devastation of cultivated land by floodwaters in the time of Noah. Thus the psalm concludes by recalling the tremendous destruction of the Flood — “God sat enthroned at the Flood” (29:10) — a destruction that cleansed the world of all that was irretrievably evil.
What does all this have to do with the Sabbath? We mistakenly think that our greatest achievements are to be found in our actions and practical accomplishments. Idleness and inactivity are assumed to be inconsequential, if not negative, aspects of life.
In truth, it is rest that perfects all actions. Rest is a contemplative process that gives meaning and purpose to our endeavors. This is the value of menuchah, the spiritual rest on the Sabbath day. It deepens our intellectual awareness and enhances our spiritual life. The Sabbath rest crowns our weekday activities, directing them toward their true purpose.
Now we may understand why the Sabbath Amidah prayer contains seven blessings. The number seven incorporates six — corresponding to the six days of creative activity — plus an additional seventh dimension of direction and purpose (cf. Maharal, Tiferet Yisrael, ch. 40). The seven blessings of the Sabbath Amidah teach that the menuchah of Shabbat is not just a negative quality, a cessation from productive work, but rather the development of our moral faculties and spiritual direction, cultivating our closeness to God and His ways.
(Silver from the Land of Israel, pp. 31-33. Adapted from Olat Re’iyah vol. II, pp. 19-20; Ein Eyah vol. I on Berachot 29a (4:43))