What do you mean, everything is hidden? I wish you good health.

It means wishing the king good health and all the best. In this greeting, "Everything is hidden" means that everything in the world is hidden and belongs to peace. It also means that the king cultivates self-cultivation and makes the people live and work in peace and contentment. And "May you be healthy" is a direct expression of blessing to the king, wishing him good health and a safe life.