There are at least two main messages being delivered to readers in “The Interlopers.” First, the author is trying to tell us that it is important to let go of our grievances before it is too late. Second, the author is trying to show us that the plans that human beings make can easily be upended and destroyed by nature or, perhaps, by fate.
In this story, von Gradwitz and Znaeym hate each other for no good reason. Their hatred has come about because of a lawsuit between their grandfathers. Because of this event that really had nothing to do with them, they hate each other enough to go out on this stormy night, hoping for the chance to kill one another. Once the tree falls on them, they come to realize that they actually have things in common and that there is no reason for them to hate one another. Sadly for them, they are not able (we assume) to make good on this reconciliation because they are going to be killed by the wolves. This is meant to show us that we need to let go of our private little hatreds before they end up destroying us. We need to give them up while we are still able to do so.
Secondly, this story is meant to show us how futile it is, in a way, for humans to make plans. The two men in this story are thwarted by nature not once, but twice. First, the tree falls on them, preventing them from trying to kill one another. Then, the wolves come, presumably preventing them from helping one another and becoming friends as they plan to do. This imparts to us the idea that our human hopes, dreams, and plans can be blown apart by forces larger than ourselves.