After Ed figures out how to help the people on the first card, he thinks he's figured out the game. Think again, Ed. The next card doesn't have addresses or names, and instead features a little riddle:
say a prayer at the stones of home. (2.3.42)
At first Ed's not sure where these stones are and thinks they could be anywhere, but then he's led to them one night.
So what's the deal? The stones of home were Ed's secret hiding place or refuge with his bro when he was younger, so it makes sense that the mystery man would include them. The stones are a symbol of something secret and private that only Ed and his brother know… and apparently somehow the guy controlling the cards knows about them too, which he totally wants Ed to notice.
Now we know that mystery dude is either the author or another godlike character (check out his write-up in the "Characters" section for more on this), but it's important to note that Ed is super confused by the fact that someone knows him so well that they even know about the stones of home. Once Ed figures out what the stones of home are, that is. And this brings up two important points: Ed can't fathom the idea that someone really knows him, and home isn't an immediately recognizable reference for the poor guy.
Ed has never quite settled into his life, has never quite felt at home with himself or other people, and the stones of home remind us of just how lost and lonely our main man is.