Bible teaches that Christ is king.

But why a king? Why not some other job?

He would be a very good scientist, just because he already knows everything. He would head such projects as building thermonuclear reactors or designing fast microprocessors. But instead he has set to become a king over the Earth.

Be assured that he chooses for himself the most efficient occupation. In Bible a king not only gives decrees but also judges. The function of a biblical king is to control the society to live in peace.

Without peace microprocessors and nuclear fusion reactors are useless. A war could destroy them anyway. The task of Christ as he rules over the Earth is to keep peace. And this task keeps him busy fulltime.

This is the reason why he is a king, not a microprocessor designer. If the peace is kept people could gradually build better microprocessors and fusion engines. If progress faced too quickly, it could lead to discrepancy between the technology and morality. Christ does not want such a discrepancy, but namely this would happen, if he would design or technology by himself thus advancing it too quickly.

Thus he has chosen the (humbly) task to be a king.