2. In every successive movement there is some medium between the extremes. But between being and not-being, which are the extremes in creation, there can be no medium, and therefore no succession.
3. In every making, in which there is succession, the process of being made is before the state of achieved completion. But this cannot happen in creation, because, for the process of being made to precede the achieved completion of the creature, there would be required some subject in which the process might take place. Such a subject cannot be the creature itself, of whose creation we are speaking, because that creature is not till the state of its achieved completion is realised. Nor can it be the Maker, because to be in movement is an actuality, not of mover, but of moved. And as for the process of being made having for its subject any pre-existing material, that is against the very idea of creation. Thus succession is impossible in the act of creation.
5. Successive stages in the making of things become necessary, owing to defect of the matter, which is not sufficiently disposed from the first for the reception of the form. Hence, when the matter is already perfectly disposed for the form, it receives it in an instant. Thus because a transparent medium is always in final disposition for light, it lights up at once in the presence of any actually shining thing. Now in creation nothing is prerequisite on the part of the matter, nor is anything wanting to the agent for action. It follows that creation takes place in an instant: a thing is at once in the act of being created and is created, as light is at once being shed and is shining.
2.18 : Solution of Arguments against Creation
2.21 : That it belongs to God alone to create