Sustaining is an act: it mediates between Relating and Relation, ensuring their joint persistence within Relational Form.
Given that Relational Form is determined by determining Relating and Relation, it cannot not derive a dynamic of determination: Sustaining. The form formalizes the interplay of Relating and Relation, but it does not itself ensure that interplay persists. Something must actively maintain and mediate between the act and the condition, ensuring their joint persistence within the form. Sustaining is this mediating act.
Sustaining produces Self-Coherence — the condition in which Relating and Relation are not merely maintained together but stabilized as a unified dynamic. Self-Coherence in turn produces Closure.