Christoph Theobald is a Jesuit, theologian, musician and musicologist, as well as an expert on the German composer. So he explained to so called Bach theology.
Bach's compositions are deeply inspired on the interprations of faith from Martin Luther, and hence, were easily adapted to Protestant liturgy. An example is the motet, Jesus meine Freude, which can be translated as Christ is my joy.
"In addition to Martin Luther, Bach was also influenced by the readings of scriptures he considered decisive. He had the Calov Bible, which at that time was more widely used, and he wrote notes and comments on it.”
Over time Bach became one of the masters in classical music, whose musical compositions are also considered today masterpieces that will never lose their artistic value.