I answer that, It is absolutely true that God is not a body; and this can be shown in three ways.
Thirdly, because God is the most noble of beings. Now it is impossible for a body to be the most noble of beings; for a body must be either animate or inanimate; and an animate body is manifestly nobler than any inanimate body. But an animate body is not animate precisely as body; otherwise all bodies would be animate. Therefore its animation depends upon some other thing, as our body depends for its animation on the soul. Hence that by which a body becomes animated must be nobler than the body. Therefore it is impossible that God should be a body.
I didn’t grasp St. Thomas’s point on the first reading, or the second. So the body’s animation depends on something nobler than itself. So what? That doesn’t take away from God’s nobility, since the thing that animates the body, the soul, would also be God — God would be a composite of body and soul, as we are, so both body and soul would be God. If God were said to be body only, then I could see Thomas’s point.
On the third reading I put two and two together: First he says that God is the most noble of beings. Then he says that the body is made animate by a more noble thing, the soul. If a soul is nobler than a body, then the most noble of beings could be a soul, but it could not be a body. In other words, a being who is soul but not body, would be nobler than a being who is body and soul. Since God is the most noble of beings, he must be soul and not body.