It’s ironic, isn’t it, that someone who doesn’t believe that God even exists gets very upset whenever God is mentioned! Wouldn’t it be more logical for him to simply smile and ignore any mention of God? It’s almost as if he’s secretly afraid God does exist, and he’s allergic to Him. But how can you be allergic to something that doesn’t even exist (at least according to him)?
Be that as it may, I hope you can find an opportunity to tell him that you didn’t mean to offend him; you sincerely thought he might enjoy the concert. And if God opens the door, ask him when and why he decided to become an atheist. Not every atheist, I’ve found, has a logical reason for his or her unbelief. Some, for example, are simply reacting against their parents’ religious convictions.
Avoid arguing with him, however; it seldom gains anything, and may only make him more defensive and close-minded. Instead, ask God to help you be an example to him of Christ’s character and love. As I’ve often said, people may argue with what we say, but they can’t argue with the testimony of a changed life.
Most of all, pray for this individual. Only God can break through the barriers of unbelief he’s erected, and only God can convict him of his need of Christ. Let Paul’s prayer become yours: “Pray … that God may open a door for our message” (Colossians 4:3).