J. S. Bach did some truly amazing things in his lifetime, not the least of which was writing a significant number of motets for use throughout the church year. These motets were typically for four-part choir, sometimes four-part-plus-four-part double choir, and sometimes five-part choir. These were generally accompanied by a small string orchestra or by organ, but since all the accompaniment typically did was double the vocal parts, these pieces are equally effective, some would say more effective, when sung unaccompanied.
What has happened here is to take a couple of small sections of Bach's best-known five-part motet, Jesu Meine Freude, BWV 227, and arrange them for string orchestra. This piece can also be used as accompaniment for the SSATB version.
Bach's work was for a choir with two soprano sections, alto, tenor and bass, which translates well to three violin parts, viola, and cello. The bass part generally doubles the cello.
The minimum voicing for this piece is three violins, a viola, and a cello. If there is no cello, the bass would play the cello part rather than the bass part. There is also an alternate bass clef version of the viola part to make it easier to double it with cello.
This piece is not for the faint of heart, and if your browser is equipped to play the midi sample, you will hear why. The fugue has numerous passages in all parts of six-to-eight-count sixteenth-note runs at about 75 beats per minute. As you might expect, Bach has these runs reversing direction and breaking into interval jumps all over the place. They are playable by strong players on all of the instruments named, but considerable rehearsal and practice time will be required to clean up the piece and develop the ensemble needed to stay together.
The chorales are much easier to play, but they would probably not work especially well as a standalone concert piece without the fugue.
FUGUE AND TWO CHORALES OF J. S. BACH, arranged for string orchestra by Tom Kirkland, comes in a pdf file of 1389K, with a ten-page score, six two-page parts, a two-page alternate part, and a license page, twenty-five pages in all. Performance time should be about 4:20.