Soverick admitted to himself, "I will admit that the first sage fooled me. He made me swear not to harm the plane. I foolishly believed that he cared about the plane. I focused on that instead of wondering why he would use a weak person as child of the plane."
He feels like a fool now. All of this time, he has believed that harming the Virut plane would affect the first sage. That's why he leaked some information to the Vipers. But he was wasting his time doing that. The one person he should have been focused on was Salvini, but he thought she was useless.
Now he understands why the first sage wanted someone from his lineage to be the child of the plane. If he were still the child of the plane, he would have too much power in his hands and be difficult to control.
Soverick lamented, "As usual, the first sage beats me in the aspect of foresight."