For an object at rest on a flat table, static friction is zero. If you push horizontally with a small force, static friction establishes an equal and opposite force that keeps the book at rest.

As you push harder, the static friction force increases to match the force. Eventually maximum static friction force is exceeded and the book moves.

The maximum static friction force is: (f_s)_max = μ_s N where μ_s is the coefficient of static friction.

Static friction is subtle because the static friction force is variable and depends on the external forces acting on an object. That is,   f_s ≤ μ_s N, while (f_s)_max = μ_s N.

In general, μ_s ≥ μ_k. It is harder to move a stationary object than it is to keep a moving object in motion.