Why the Scholar Fit to Rule on Law Comes from Levi and Issachar

Rava said: You will not find a young scholar who renders legal rulings except one who comes from Levi or from Issachar. From Levi, as it is written, "They shall teach Your judgments to Jacob" (Deuteronomy 33:10). From Issachar, as it is written, "And of the children of Issachar, men who had understanding of the times" (1 Chronicles 12:32). And should you say, perhaps also from Judah, as it is written, "Judah is my lawgiver" (Psalms 60:9)? [No, for there it means rulership and kingship.] I am speaking of drawing out a teaching in accordance with the settled law.