Shape (shakl) concerns an external configuration such as roundness or rectangularity. By contrast, corporeal form accounts for bodily extension and specific form for belonging to a kind.
Clay made into a cup or a brick changes shape. Such change does not itself prove the creation or eternity of a philosophical underlying substance. Similarly, members of one kind may differ in shape while remaining members of that kind.
Confusing accidental configuration with specific nature or underlying substrate distorts arguments concerning origination and eternity.