His help? As things to say to Ben went, it was a very good call, as Ben had the Winchester genetic urge to do the right thing and his father's same dedication to do his part when it was needed. And Castiel was saying his part was needed.
Ben straightened then, that same sort of 'I'm a little man' posture, and he nodded. Something constructive to do, an actual mission. Ben didn't know how he'd do it yet, as his uncle was rarely home, but it was at least something to think about. In the face of no longer knowing how he felt about Ruby or what to do about her, he'd just focus on Sam.
"Dude, I'm on it," he said with a sharp, determined nod.