Luke 24:16

But their eyes were holden that they should not know him. And he said unto them, What communications are these that ye have one with another as ye walk? And they stood still, looking sad.

It was so incredible, in the view of these two, that any person whosoever in the environs of Jerusalem should have been unaware of the stupendous events unfolded there so recently, or that such a person would not have known anything about them, that they stopped walking, astounded at what appeared to them incredible. Of course, Jesus did know all about those events, far more than they knew; nor was Jesus' question here for the purpose (a) either of procuring information for himself, or (b) of professing any need of enlightenment from them. It was a means of inviting himself into the conversation which had evidently continued for some little while after Jesus fell in step with them. God asked Adam, "Where art thou?" not to procure information but to induce a confession.