Grantaire continued to scan the book until Enjolras was settled. It was a weighty topic, and if the circumstances had been any different, Grantaire would say he'd already had enough of its nonsense. He was doing this-- only this small thing-- because he was afraid that Enjolras was dying and would leave him to this world alone. The rest of his friends were fun to be around, but without their leader, who were they? Who was he? Grantaire didn't want to think about it. That's one of the reasons he drank.
Once Enjolras was sitting up a little (and Grantaire made sure he was able to breathe as well as possible), without pretense or preamble, he began reading aloud. Grantaire's voice was surprisingly sure of itself, clear and eloquent. His near-sobriety lending a knowledgeable demeanor to the reading. The drunk was surprisingly effective when he wanted to be, and since Enjolras didn't have the strength to be impassioned himself, it was the very least Grantaire could do on his behalf.
In truth, Rousseau himself annoyed Grantaire just as much as he seemed to delight Enjolras, but such a difference of opinion is the way the two friends operated. He fought to keep the scepticism from his voice but failed miserably at times.