The book’s qualification “unless evidence indicates otherwise” governs the interpretation of every imperative. A valid indicator can move the command away from its ordinary obligatory force.
Depending on evidence, an imperative may communicate recommendation, guidance, or permission. These readings cannot be chosen merely to suit a preference: the context or an additional proof must justify them.
For comparison, “Perform the prayer” and a conversational “Sit down and rest” have different force because their setting and supporting indications differ.