Chovos Halvavos reaches a turning point in the Hakdamah: why did Rabbeinu Bachya write this sefer? After surveying the great Torah works that already existed — on Tanach, Halacha, and Emunah — he discovered a surprising omission: there was no comprehensive work devoted to the duties of the heart.

Could it be that these inner obligations are merely good advice rather than actual mitzvos? That's the question that sets the stage for what comes next.