 This leaves only a couple of missing arias, which are taken from other Bach works when reconstructions are attempted.However, since Bach's recitative is lost, most reconstructions use the recitatives composed for a "Markus-Passion" attributed to Reinhard Keiser, a work which Bach himself performed on at least two occasions, which gives a certain authenticity to things, although it could be viewed as somewhat disrespectful to Keiser's work.However, Keiser's setting starts slightly later than Bach's, which requires a small amount of composition on the part of the reconstructor.