Trinity’s organist, Avi Stein, will lead Trinity Choir and Trinity Baroque Orchestra in one of Bach’s most monumental works — the Mass in B Minor (Part 1: Kyrie and Gloria). In this selection from the magnum opus, aficionados will recognize references to earlier compositions. Such a retrospective is sure to underscore Johannes Brahms’s famous decree: “Study Bach, there you will find everything.” The Mass will be performed on October 29.