Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Make verbs consistent in mood and voice
Eliminate distracting shifts
Clarity

Unnecessary shifts in the mood of a verb can be distracting and confusing to readers. There are three moods in English: the indicative, used for facts, opinions, and questions; the imperative, used for orders or advice; and the subjunctive, used to express wishes or conditions contrary to fact (see 27g).

The following passage shifts confusingly from the indicative to the imperative mood.

A verb may be in either the active voice (with the subject doing the action) or the passive voice (with the subject receiving the action). (See 8a.) If a writer shifts without warning from one to the other, readers may be left wondering why.