Paraphrasing the Summa: First part, Question 1, Article 7

Question 1: The nature and extent of sacred doctrine.

Is Christian doctrine revealed by God?  Does it teach us about the supernatural as well as the natural?

Article 7. Whether God is the object of this science?

Does Christian doctrine teach us about God?

Objection 1. It seems that God is not the object of this science. For in every science, the nature of its object is presupposed. But this science cannot presuppose the essence of God, for Damascene says (De Fide Orth. i, iv): "It is impossible to define the essence of God." Therefore God is not the object of this science.

It is impossible that any body of knowledge could teach us about God, since even the Saints admit that God is unknowable.  St. John of Damascus, in his book, also says, ""It is impossible to define the essence of God."

Therefore, the first objection claims, that Christian doctrine can not teach us about God.

Objection 2. Further, whatever conclusions are reached in any science must be comprehended under the object of the science. But in Holy Writ we reach conclusions not only concerning God, but concerning many other things, such as creatures and human morality. Therefore God is not the object of this science.

In addition, Christian doctrine teaches about many things.  As an example, Sacred Scripture treats of animals and men and right and wrong.  Therefore, Christian doctrine is not about God.

On the contrary, The object of the science is that of which it principally treats. But in this science, the treatment is mainly about God; for it is called theology, as treating of God. Therefore God is the object of this science.

St. Thomas retorts that all sciences have a main object, as well as, subordinate objects.  Christian doctrine is mainly about God.  That is why it is also known as THEOLOGY.  Which, broken down to its etymology, means, "The Logos (Word) of God."

I answer that, God is the object of this science.

Therefore, St. Thomas, stringently reiterates that Christian doctrine is a science whose purpose it is to explain the essence of God.

The relation between a science and its object is the same as that between a habit or faculty and its object.

 A faculty is an ability, like sight.  So, the relationship between sight and that which it is observing.  Is the same as that of a science to that which it is studying.

Now properly speaking, the object of a faculty or habit is the thing under the aspect of which all things are referred to that faculty or habit, as man and stone are referred to the faculty of sight in that they are colored. Hence colored things are the proper objects of sight.

 The eye observes color in all things because color is common to all things.

But in sacred science, all things are treated of under the aspect of God: either because they are God Himself or because they refer to God as their beginning and end.

Christian doctrine observes God in all things.  Either because it is studying God, directly.  Or because it is something which is made by God and will return to God.

Hence it follows that God is in very truth the object of this science.

Therefore, God is the object of Christian doctrine, as color is the object of sight.

This is clear also from the principles of this science, namely, the articles of faith, for faith is about God.

This is confirmed in the summaries of that which we believe, in the Creeds.  These are summaries of that which is taught in Christian doctrine and every element of the Creeds is about God.

The object of the principles and of the whole science must be the same, since the whole science is contained virtually in its principles. Some, however, looking to what is treated of in this science, and not to the aspect under which it is treated, have asserted the object of this science to be something other than God — that is, either things and signs; or the works of salvation; or the whole Christ, as the head and members. Of all these things, in truth, we treat in this science, but so far as they have reference to God.

Christian doctrine treats of many things.  But only as they relate to God and His will for mankind.

Reply to Objection 1. Although we cannot know in what consists the essence of God, nevertheless in this science we make use of His effects, either of nature or of grace, in place of a definition, in regard to whatever is treated of in this science concerning God; even as in some philosophical sciences we demonstrate something about a cause from its effect, by taking the effect in place of a definition of the cause.

The first objection says that God can't be known.  Therefore, there can exist no science which tells us about God.

But, St. Thomas says, although God can not be understood completely, there are some things about Him which we can understand know by the effects of that which He has done and by that which He has revealed.

Reply to Objection 2. Whatever other conclusions are reached in this sacred science are comprehended under God, not as parts or species or accidents but as in some way related to Him.

The second objection says that Christian doctrine treats of too many things to be about God.

But St. Thomas says that all those things are treated of, as they relate to God.  In Christian doctrine, nothing is treated of as separate from God.