Schelling's attempt to explain creation in terms of nature's "ground" and "existence" is a seminal moment in his thinking. It is by no means surprising that he would turn to Plato's Timaeus to develop that distinction in a type of philosophy of organism or "organicism," which Plato himself had developed implicitly in the Republic and rather explicitly in the Timaeus. Schelling, modeling his own philosophy of organism upon this, makes the most concrete statement of his position in this commentary.
As an aside, for awhile now I've been considering how Schelling and Plato both inform each other's metaphysics in light of what I call an "ecological metaphysics," something extremely valuable in contemporary Continental environmental philosophy, whether through environmental aesthetics, environmental hermeneutics, or semiotic phenomenology - the key being the disclosure, experience of, and interpretation of natural signs and sign processes in the natural world, e.g. Jasperian "cyphers" in light of holistic and inter-related context.
Continental environmental philosophy hasn't had current meaningful developments since Erazim Kohak's Green Halo and The Embers and the Stars. While much has been done with Merleau-Ponty, or Merleau-Ponty and Schelling together - a task which has by now become rote and shopworn - I think the time is ripe for a fresh perspective, perhaps with the development of this "ecological metaphysics" directly using Plato and Schelling.
Just food for thought.
Link to Schelling's commentary on the Timaeus HERE.