Kong is the intermediary. While not the most important by any means, he will coordinate and prepare the marine, ciper pol, seraphim, impel down, holy knights, gorosei and imu for the final war.
kind of a baron tomago like role in the final war.
In a war scenario I imagine whoever takes him down will cause the world government to lose all coordination in the final war. If he goes down everything goes to shit for the world government.