What was Les alluding to that upset the caller?
The teaching was an eternal security for the true believer. The caller from Oklahoma, though not angry, was a little upset that this doctrine was being alluded to before it had been stated as boldly as it later would be.
Les explains that when he had been on the Tulsa station only a month or two, a gentleman from Oklahoma called. The man was not angry but was a little upset because Les had been alluding to an eternal security for the true believer. Les admits he had not yet come out as boldly as he has since. The caller challenged him, asking, "How can you do that?" This ties to the Corinthians example: Paul says they would be confirmed to the end and stand blameless before God, not because they were blameless, but on the basis of grace.