The scepter shall not depart from Yehudah, this refers to kingship. 

R' Simeon b Yohai said:  Why was Yisrael compared to a vine? (Yeshayahu 3:7) When you sow a plant in the ground, its place is distinct.  So did the Holy One, blessed be He, plant kingship in the Tribe of Judah [for all time], until the King Mashiach will blossom forth.  The "ruler's staff" refers to the Nasi [Head or Prince, the official title of the head of Palestine Jewry after the overthrow of the Jewish Kingdom]. Until when?  "Until Shiloh comes;" which means, until the Nasi comes and restores the kingdom to David; as it says:  My servant David [shall be] prince (nasi) among them (Yechezkel 34:24).