The good is still abstract. It does not say what exactly to do. Who decides then?

The inner self of the person. He is certain of himself. He determines what is good here and now. He decides. We call this inner authority conscience.

What is special about conscience?

In conscience, a person is wholly with himself. It is a deep inner solitude. Everything outward falls away. No command and no tradition counts, only his own knowing. In earlier times, people had a law or a religion outside themselves. Conscience, by contrast, knows: Only my own thinking binds me.

This is a high standpoint. It belongs to the modern age.

Why is duty not enough?

People can talk about duty in lofty words. That makes the heart grow wide. But in the long run it becomes boring. Spirit wants to know what it should actually do.

Summary: Because the good is abstract, conscience decides. It is the inner certainty of the person, which determines for itself. This is a high standpoint of the modern age.

§ 511. The all-round contradiction which this manifold ought, the absolute being that is nevertheless at the same time not, expresses, contains the most abstract analysis of spirit within itself; its deepest going into itself. The relation of the self-contradicting determinations to one another is only the abstract certainty of itself, and for this infinity of subjectivity the universal will, the good, right and duty, equally is as also is not; it is this certainty that knows itself as that which chooses and decides. This pure certainty of itself, raised to its extreme point, appears in the two forms, passing immediately into one another, of conscience and of evil. The former is the will of the good, which, however, in this pure subjectivity is the not-objective, not universal, the unsayable, and concerning which the subject knows itself in its singularity as deciding. The evil, however, is this same knowledge of its singularity as that which decides, insofar as it does not remain in this abstraction, but gives itself, against the good, the content of a subjective interest.

§ 511. The all-round contradiction which this manifold ought — the essential being that is nevertheless at the same time not — expresses, contains the most abstract analysis of spirit within itself, its deepest going into itself. The relation of the self-contradicting determinations is only the abstract certainty of itself, the infinity of subjectivity, for which the universal will, the good, right and duty equally is and is not, and which knows itself as that which chooses and decides. This pure certainty of itself, raised to its extreme point, appears in the two forms, passing immediately into one another, of conscience and of evil. The former is the will of the good, which, however, in this pure subjectivity is the not-objective, not universal, the unsayable, and concerning which the subject knows itself, in its singularity, as deciding. Evil, however, is this same knowledge of its singularity as that which decides, insofar as it does not remain in this abstraction, but gives itself, against the good, the content of a subjective interest.

§ 426. The all-round contradiction which this manifold ought expresses is the most abstract analysis of spirit, its deepest going into itself. The pure relation of the self-contradicting determinations is the abstract certainty of itself, the infinity of subjectivity, for which the universal will, the good, right and duty equally is and is not, and which knows itself as that which chooses and decides.