هَلَكَ عَنِّي سُلْطَانِيَهْ (My power has gone from me for good...69:29). The word sultan, literally, yields the sense of 'power or overpowering'. Therefore, a government or state is referred to as saltanah and a ruler is referred to as sultan. In other words, when people gain power and political ascendancy in the world, they become proud, hold sway over other people, perpetrate injustices and commit atrocities. But in the Hereafter all that will vanish and be lost, and the unjust and proud rulers will have no army to obey or support them. They will be miserable and helpless creatures who will not be able to defend themselves.
The word sultan also stands for 'authority, proof or argument' in which case it would mean: 'Today I have no argument in favour of protecting myself against punishment'.