هَوَاهُ contains the noun هَوًى (“desire”) and the attached pronoun ـهُ (“his”). تَبَعًا conveys following: desire should not become the final authority over sound guidance.
حَتَّى يَكُونَ means “until it becomes.” The negative opening points toward this required change in a person’s outlook.
For example, before acting on anger, one can identify the relevant principle and choose accordingly. Following guidance is measured by such conduct, not merely by repeating a statement.