Abstract: The presence of certain motifs associated with pietism in the music of J. S. Bach has led some scholars to conclude that the composer was profoundly influenced by the 17th century movement within the German Lutheran Church. This essay argues that Bach was a Lutheran theologian, whose works can be understood only in the closest relationship to Martin Luther. Bach's commitment to Lutheran orthodoxy is evidenced by his erudite grasp of the writings of Luther and his long friendship with Eerdmann Neumeister. But it is in his music that Bach shows himself to be the true heir of the Lutheran tradition. This essay examines Bach's commitment to Scripture, his Christology and his soteriology.