Objection: a command appears to require an addressee who can understand and perform it. How could an eternal command concern persons who do not yet exist?
The reply distinguishes eternity of the attribute from the addressee's becoming liable to it at the appropriate time. An eternal command may concern someone who later becomes capable of being addressed. The attribute need not begin when the addressee comes into existence.
A father may set out an instruction intended for a child when the child reaches maturity. This human analogy illustrates temporal applicability; it does not suggest that God acquires a new intention or plan.