In truth, he does not know what to say to this. He wants to say that they have more control than that -- but he doesn't know that to be true. He has thought, before, that he was sure enough of what would happen here and has been wrong. He doesn't know any more about the powers in charge here than he did before he came; he only knows that he cannot always choose and that they must bear up under what comes their way.

He suspects that none of this would comfort Susan.

In the absence of anything that feels useful to say, he nods. If nothing else, he understands her sentiment. After a moment he says, "I will do whatever I can for thee. To aid thee. I am thine."