This piece is based on material from Bach's motet Jesu Meine Freude, BWV 227 Number VIII, So aber Christus in euch ist.
The text of this movement is Romans 8:10-- "If now Christ Jesus lives in you, although the body is dead because of sin, the Spirit is life because of righteousness."
In the motet, this piece appears in C major, voiced for alto, tenor, and bass. It ends with an E major chord to set up the chorale fantasy that follows. This means that it would be almost useless to present this as a straight transcription as the ending would be quite unsettling to the listener. The "fix" was to remove the final phrase and splice a modification of the opening phrases in its place returning the piece to its starting key. This version is written in F major to stay within the working ranges of the three instruments.
There is no workaround for the bass trombone, though this piece could possibly be performed with two euphoiums and a tuba. Other possibilities would be three bassoons or three cellos, ("bass" cello will use the open C string).
IF NOW CHRIST JESUS LIVES IN YOU, by J. S. Bach, arranged by Tom Kirkland for trombone trio consisting of two tenors and a bass, comes in a pdf file of 524K, a four-page score, three two-page parts, and a license page, eleven pages in all. Performance time should be about 2:15.