There is at least one book on this piece:
J. S. BACH'S MUSICAL OFFERING. By Hans Theodore David. (G. Schirmer, Inc., New York, I945. Pp. xi, 190.)
And some people believe that this works is "one of his greatest, and perhaps least understood, works" !
"In 1747, Bach went to the court of Frederick II of Prussia in Potsdam, where the king played a theme for Bach and challenged him to improvise a fugue based on his theme. Bach improvised a three-part fugue on Frederick's pianoforte, then a novelty, and later presented the king with a Musical Offering which consists of fugues, canons and a trio based on the "royal theme", nominated by the monarch. Its six-part fugue includes a slightly altered subject more suitable for extensive elaboration.
Orchestral and chamber music
Bach wrote music for single instruments, duets and small ensembles. Bach's works for solo instruments—the six sonatas and partitas for violin (BWV 1001–1006), the six cello suites (BWV 1007–1012) and the Partita for solo flute (BWV 1013)—may be listed among the most profound works in the repertoire. Bach also composed a suite and several other works for solo lute. He wrote trio sonatas; solo sonatas (accompanied by continuo) for the flute and for the viola da gamba; and a large number of canons and ricercare, mostly for unspecified instrumentation. The most significant examples of the latter are contained in The Art of Fugue and The Musical Offering.
Bach's best-known orchestral works are the Brandenburg concertos, so named because he submitted them in the hope of gaining employment from Margrave Christian Ludwig of Brandenburg-Schwedt in 1721; his application was unsuccessful. These works are examples of the concerto grosso genre. Other surviving works in the concerto form include two violin concertos (BWV 1041 and BWV 1042); a Concerto for Two Violins in D Minor (BWV 1043), often referred to as Bach's "double" concerto; and concertos for one, two, three and even four harpsichords. It is widely accepted that many of the harpsichord concertos were not original works, but arrangements of his concertos for other instruments now lost. A number of violin, oboe and flute concertos have been reconstructed from these. In addition to concertos, Bach also wrote four orchestral suites, a series of stylised dances for orchestra, each preceded by a French overture. The work now known as the Air on the G String is an arrangement for the violin made in the nineteenth century from the second movement of the Orchestral Suite No. 3."