Cantata 107, composed in 1724 in Leipzig, is one of my favorites. Based on the unchanged words of a hymn in seven stanzas by Johann Heermann, scholars surmise that Bach was challenging himself by choosing to adhere to the exact text of each of the seven stanzas in the seven movements of this cantata.
In spite of (or because of?) his self-imposed limitations, Bach creates an exquisitely beautiful work with great depth and variety. I particularly love the 6th movement which features a solo tenor and two unison flutes.
Enjoy this recording by the Bach Collegium Japan conducted by Masaki Suzuki with Makoto Sakurada, tenor.