THE FUNCTION OF FIRSTBORN, KING AND PRIEST IS SPLIT AMONG THE TRIBES OF ISRAEL

Midrash Rabbah - Genesis 98:4

REUBEN, THOU ART MY FIRSTBORN (Genesis 49:3) … THE EXCELLENCY OF DIGNITY, AND THE EXCELLENCY OF POWER:

the birthright should have been yours, priesthood yours and royalty yours. Now that you have sinned, however, the birthright has been given to Joseph, the priesthood to Levi, and royalty to Judah.