When I first considered becoming a cantor, my teacher and mentor Cantor Stephen Berke described hazzanut (cantorial music) as being "like jazz," in the sense that the cantor, like the jazz musician, has a range of motifs at his/her disposal and can use them improvisationally at will. Some time into my cantorial studies, I discovered that Jewish music and liturgy has its own form of blues. It's called Selihot, the series of prayers that are recited (in Ashkenazi tradition) from the week before Rosh Hashanah until Yom Kippur. On Yom Kippur itself, the Selihot segment is recited a total of five times.
Like the blues, Selihot has a particular musical form. Also like the blues, the liturgical themes are quite limited - seeking forgiveness for our transgressions, praising God and highlighting God's merciful qualities, confessing aloud the things we have done wrong. And, like the blues, the themes are endlessly variable - not only have payyetanim (Jewish liturgical poets) crafted many Selihot prayers over the centuries, but there is always an opportunity for personal improvisation as well.
While it might be inappropriate to suggest that we prepare for the Aserete Yemei Teshuvah (the Ten Days of Repentance) by listening to scratchy old records of blues rabbis like Robert Johnson or Muddy Waters, it is certainly a good idea to pick up a High Holiday mahzor (prayerbook) and scan through the classics of Selihot: Haneshamah Lakh ("The Soul is Yours), Shema Qoleinu ("Hear our voices"), and that old standby, the Thirteen Attributes of God:
Adonai, Adonai, God, merciful and compassionate, patient, abounding in love and faithfulness, assuring love for thousands of generations, forgiving iniquity, transgression, and sin, and granting pardon.