Derech Hashem, Part 4, Ch. 2 – 46

Besides the difference in the blessing learners receive, as the higher the level of learning, the higher and stronger the spiritual effect has on the person learning, there is also a difference in its effect on the world, and there is no learning that doesn’t have some effect on some part of creation. From this we can understand that a person should learn all parts of the Torah to the best of his ability, in order to bring the most perfection to the world. However, the amount a person should invest in each part of the Torah depends on his qualities and his environment.