Paraphrasing the Summa: First part, Question 1, Article 4

 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 4. Whether sacred doctrine is a practical science?

Is Christian doctrine an applied science?  In other words, is Christian doctrine a body of knowledge which teaches how to apply true sciences to solve problems?

Objection 1. It seems that sacred doctrine is a practical science; for a practical science is that which ends in action according to the Philosopher (Metaph. ii). But sacred doctrine is ordained to action: "Be ye doers of the word, and not hearers only" (James 1:22). Therefore sacred doctrine is a practical science.

 The first objection uses Scripture to designate Christian doctrine merely as a body of knowledge which teaches us how to overcome problems.

Objection 2. Further, sacred doctrine is divided into the Old and the New Law. But law implies a moral science which is a practical science. Therefore sacred doctrine is a practical science.

Christian doctrine is divided into Old and New Law.  Law implies justice and ethics.  These are practical applications of life.  Therefore, Christian doctrine is not a true science, but an applied science, like Engineering which uses mathematics and other sciences to design vehicles, dwellings and roads.

On the contrary, Every practical science is concerned with human operations; as moral science is concerned with human acts, and architecture with buildings. But sacred doctrine is chiefly concerned with God, whose handiwork is especially man. Therefore it is not a practical but a speculative science.

A speculative science is not one which "speculates" in the sense of guessing or hoping.  A speculative science considers that which is true but does not apply it to mundane problems.

St. Thomas says that applied sciences deal with human creations.  And moral sciences deal with human behavior.  But Christian doctrine deals with God and God's creations, especially man.   Therefore it is not a practical or applied science, but a speculative science.

I answer that, Sacred doctrine, being one, extends to things which belong to different philosophical sciences because it considers in each the same formal aspect, namely, so far as they can be known through divine revelation. Hence, although among the philosophical sciences one is speculative and another practical, nevertheless sacred doctrine includes both; as God, by one and the same science, knows both Himself and His works. Still, it is speculative rather than practical because it is more concerned with divine things than with human acts; though it does treat even of these latter, inasmuch as man is ordained by them to the perfect knowledge of God in which consists eternal bliss. This is a sufficient answer to the Objections.

In this case, St. Thomas does not address each objection individually, but addresses them with one general response.

Essentially, he says that Christian doctrine is a speculative science which includes aspects of God's revelation which can be applied towards achieving union with God and man's salvation.