Paraphrasing the Summa: First part, Question 3, article 1

Article 1. Whether God is a body?

Is God made like a man?  

Objection 1. It seems that God is a body. For a body is that which has the three dimensions. But Holy Scripture attributes the three dimensions to God, for it is written: "He is higher than Heaven, and what wilt thou do? He is deeper than Hell, and how wilt thou know? The measure of Him is longer than the earth and broader than the sea" (Job 11:8-9). Therefore God is a body.

Scripture says that God is three dimensional, with height, length and width.  Therefore, God is a material being, like a man or an animal.

Objection 2. Further, everything that has figure is a body, since figure is a quality of quantity. But God seems to have figure, for it is written: "Let us make man to our image and likeness" (Genesis 1:26). Now a figure is called an image, according to the text: "Who being the brightness of His glory and the figure," i.e. the image, "of His substance" (Hebrews 1:3). Therefore God is a body.

 Again, Scripture also depicts God as an image and with substance.  In fact, men were made in His image.  Therefore, God has an appearance, like a man.

Objection 3. Further, whatever has corporeal parts is a body. Now Scripture attributes corporeal parts to God. "Hast thou an arm like God?" (Job 40:4); and "The eyes of the Lord are upon the just" (Psalm 33:16); and "The right hand of the Lord hath wrought strength" (Psalm 117:16). Therefore God is a body.

Scripture also describes God's hands and eyes, therefore, God is made like a man.

Objection 4. Further, posture belongs only to bodies. But something which supposes posture is said of Godin the Scriptures: "I saw the Lord sitting" (Isaiah 6:1), and "He standeth up to judge" (Isaiah 3:13). Therefore God is a body.

Further, Scripture shows God sitting and standing.  Therefore, God has a body, like a man.

Objection 5. Further, only bodies or things corporeal can be a local term "wherefrom" or "whereto." But in the Scriptures God is spoken of as a local term "whereto," according to the words, "Come ye to Him and be enlightened" (Psalm 33:6), and as a term "wherefrom": "All they that depart from Thee shall be written in the earth" (Jeremiah 17:13). Therefore God is a body.

And finally, Scripture also says that God is in a certain place and that people come to Him and depart from Him.  Therefore, God takes up space and is limited.  Therefore, God is like a man.

On the contrary, It is written in the Gospel of St. John (John 4:24): "God is a spirit."

St. Thomas counters the objections by pointing out that Scripture also says that God is a spirit.

I answer that, It is absolutely true that God is not a body; and this can be shown in three ways.

St. Thomas says he can provide 3 proofs that God is not a material being.

First, because no body is in motion unless it be put in motion, as is evident from induction. Now it has been already proved (2, 3), that God is the First Mover, and is Himself unmoved. Therefore it is clear that God is not a body.

He points us to question 2, article 3 and says that the fact that God is the First Mover and yet is unmoved, means that He can't be limited to a material body and must be a Spirit.

Secondly, because the first being must of necessity be in act, and in no way in potentiality.

The second proof says that the First Being, God, must be pure action and can't be motionless.  Can't be waiting to move or at rest.

For although in any single thing that passes from potentiality to actuality, the potentiality is prior in time to the actuality;

In material beings, being at rest precedes moving to action.

nevertheless, absolutely speaking, actuality is prior to potentiality;

But, in reality, action precedes rest;

for whatever is in potentiality can be reduced into actuality only by some being in actuality.

because that which is at rest can only be moved by a being in motion.

Now it has been already proved that God is the First Being.

And God is the First Being

It is therefore impossible that in God there should be any potentiality.

Therefore, it is impossible that God should ever be at rest.

But every body is in potentiality because the continuous, as such, is divisible to infinity;

Now, St. Thomas throws a bit of a curve here, for me.  He jumps to the fact that bodies are limited (divisible to infinity), in time and space.   And he says that this is the reason why bodies are at rest.

it is therefore impossible that God should be a body.

 I think he means that, since God is the animator of the entire universe, He can't be limited in time and space and therefore, can't be a material being with a body, like a man.

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.

The third proof is this.  God gives life to all the universe.  And that which gives us life must be better than that which receives life.  Therefore, God who gives life to the body is not Himself a body.

*Scripture says, the Spirit gives life.

Reply to Objection 1. As we have said above (Question 1, Article 9), Holy Writ puts before us spiritual and divine things under the comparison of corporeal things. Hence, when it attributes to God the three dimensions under the comparison of corporeal quantity, it implies His virtual quantity; thus, by depth, it signifies His power of knowing hidden things; by height, the transcendence of His excelling power; by length, the duration of His existence; by breadth, His act of love for all. Or, as says Dionysius (Div. Nom. ix), by the depth of God is meant the incomprehensibility of His essence; by length, the procession of His all-pervading power; by breadth, His overspreading all things, inasmuch as all things lie under His protection.

To counter objection #1 above, St. Thomas points us to Question 1, Article 9 and says that Scripture uses metaphors and figures of speech to express many of God's attributes in a manneer which we can visualize.

Reply to Objection 2. Man is said to be after the image of God, not as regards his body, but as regards that whereby he excels other animals. Hence, when it is said, "Let us make man to our image and likeness", it is added, "And let him have dominion over the fishes of the sea" (Genesis 1:26). Now man excels all animals by his reason and intelligence; hence it is according to his intelligence and reason, which are incorporeal, that man is said to be according to the image of God.

Objection 2 says that man is in the image of God therefore, God is like a man.  But St. Thomas says that the Scripture which says that man is in the image of God is a reference to the spirit which God put into the man to animate his body.

Reply to Objection 3. Corporeal parts are attributed to God in Scripture on account of His actions, and this is owing to a certain parallel. For instance the act of the eye is to see; hence the eye attributed to God signifies His power of seeing intellectually, not sensibly; and so on with the other parts.

Again, St. Thomas says that any body parts attributed to God in Scripture, are similes and metaphors.

Reply to Objection 4. Whatever pertains to posture, also, is only attributed to God by some sort of parallel. He is spoken of as sitting, on account of His unchangeableness and dominion; and as standing, on account of His power of overcoming whatever withstands Him.

So are any positions and postures which Scripture uses to signify God's attributes.

Reply to Objection 5. We draw near to God by no corporeal steps, since He is everywhere, but by the affections of our soul, and by the actions of that same soul do we withdraw from Him; thus, to draw near to or to withdraw signifies merely spiritual actions based on the metaphor of local motion.

And finally, we don't move closer to God in time and space, but in love.  When we do those things which please Him.   We move away from God when we do not love Him or our fellow man, when we sin and do not do His will.