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.
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.
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.
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.
Source: Summa Theologica (New Advent)