Paul and Barnabas were becoming used to persecution. They were frequently being run out of town. But not at Lystra. At Lystra they were declared Gods.
The Bible routinely warns us of the temptation to play God. Paul and Barnabas recognize it. They go running into the crowd, tearing their clothes, and declaring, "we are men just like you." In what ways are we tempted to be God? What does it mean to be human?