Reassurance isn't something that comes naturally to him and there's little here to be hard; that it doesn't much work isn't anything that'd overly shock him. (Or at all.) Bothering at all is less out of sentiment than it is out of pragmatism - if she can trust him, this will be easier. On which note:

"What I'm going to do will be profoundly intimate. I'm to create something that will become a part of your mind, your spirit- something that will grow naturally into you and which I'll cede control of to you. In the process, I'll have to get rather acquainted with both mind and spirit."