BAREKHI NAFSHI (Heb. בָּרְכִי נַפְשִׁי; "Bless the Lord, O my soul"), initial words of Psalm 104. The central theme of this psalm is the glorification of God as the Creator of the universe, the majesty and beauty of which testify to the wisdom of the Master of all creatures. This psalm is regarded as one of the loftiest and most beautiful examples of ancient Hebrew poetry and a magnificent expression of monotheism. According to traditional Ashkenazi custom, this psalm is recited in private, on the afternoons of the Sabbaths between Sukkot and Passover, together with the 15 "Psalms of Ascent" (120–134). The reason for this custom may well be the analogy of this psalm with the account of creation given in Genesis and read on the Sabbath following the Sukkot festival (Shabbat Bereshit). After Passover the recitation of Pirkei*Avot replaces that of the Psalms. The praise of the Creator and the creation is also the reason why Psalm 104 is recited on New Moons after the morning service (and in the Sephardi rite also before the evening service).
Baer S., Seder, 266 ff.; Eisenstein, Dinim, 56.