Rashi in V’zois HaBerachah by the berachah of Moshe to Zevulun writes: “Zevulun is placed ahead of Yissachar, because the Torah of Yissachar came by means of Zevulun.” The implication is that Zevulun is of greater importance than Yissachar. Indeed, the calling of Shimon by the name of his brother Azaryah, gives an impression that Azaryah is the more important of the two. However, the Gemara (Berachos 17a) clearly implies (with the exception of the explanation of Rav Moshe) that the talmud chocham is of greater importance than one who supports Torah.
The Be’er Moshe (V’zois HaBerachah) offers an interesting interpretation. He explains that although Zevulun takes precedence in time, because “if there is no flour, there is no Torah,” nevertheless, Yissachar takes precedence in order of importance. He goes on to quote from the Medrash (Bamidbar Rabbah 2:7) that the clothing of Yissachar is black, whereas that of Zevulun is white. The difference between the two is the difference between the black letters of Torah, and the white parchment that permits its revelation. Although the parchment must precede the writing on it, the writing is doubtless of greater importance than the parchment on which it is written.
