Derekh Hashem, Part Four, On Torah Study

Regarding the parts of the Torah: However besides this gradation regarding the granting of reward for people's efforts according to the proper measure, there is another differentiation and division according to what requires refinement in the whole of creation. [This is the case] to the point that there is no part of it that is not refined by [Torah study]; such that a part of the creation will [always] be perfected by it. So it comes out that someone who wants to serve in front of his Creator with complete service must occupy himself with all of its parts according to his ability, so that the refinement come from him to all parts of the creation. And in this light, they, may their memory be blessed, said (Kiddushin 30a), "A man should always divide his days into three: A third for Scripture; a third for Mishnah; and a third for Gemara." And included in this are all parts of the Torah - such that one divides his time until he has reached all of them. Nor should he relinquish any of them; however the measure [of time] of his occupation in each of them is fitting to measure according to who he is and according to the events that happen to him. And we have already spoken about this in a separate essay, see there.