In addition to his Chorale Preludes and transcriptions of concertos by other composers, Walther also left us a small body of free compositions, of which 8 have survived to the present time. Three of these (Preludio con Fuga in A major, Toccata con Fuga in C major, and Variations on a basso continuo by Corelli) I've already uploaded in the past, leaving just 5 more pieces by Walther, including the present upload.
This work is not a transcription of an existing concerto, but rather an original organ composition by Walther. It is divided into five main parts. The first part is a Preludio for manuals and pedal, with a short 7 bar slow introduction leading into a short fugal allegro. The second part is a Largo for manuals only. The third part, for manuals and pedal, is labeled "Ritornello. Vivace", and is in ABA form with a central section bearing the title "Aria". The fourth part is for manuals only and labeled "Aria. Largo". The final section is a lively Vivace movement in 6/8 time for manuals and pedal.