What does apostasy mean according to the Bible?

Les teaches that apostasy is a terrible thing. Most people do not even know what apostasy means, and some wonder whether it is something the apostles taught. He explains that apostasy has nothing to do with the apostles; rather, it is turning one’s back on the revealed truth of Scripture—turning our back on the revealed truths of Scripture. In the context of Paul’s warning, Les points out that Paul was not writing out of meanness or envy but by inspiration of the Spirit, emphasizing that if the true gospel is adulterated or perverted, we are in danger of being accursed. He also notes that repetition in Scripture is there to get our attention, as when Paul repeats the warning that even an angel from heaven preaching any other gospel should be accursed.