Heresy is attractive, deeply attractive. It is the truth we all want in the way we all want it. Heresy appears to allow us to have God, Jesus, and a gospel to tell that is really good news. Inevitably heresy comes loaded with gifts, benefits and selling points, and without costs, drawbacks, or small print. People who teach heresy don't present it as anything other than gospel truth. We should not underestimate the necessity of the work of the Holy Spirit in granting us to accept and believe the gospel and to submit to the authority of Scripture. Without his work whether we embrace atheism or heresy we will still not accept the things of God and come to a knowledge of the truth.
There are two obvious points of application from this:
1. We should never be satisfied with the sound of well known words and phrases. We need to be satisfied that the meaning of those words are filled with biblical content and established historic (confessional) use. It is all well and good hearing that someone believes in the substitutionary nature of the atonement and justification by faith, but history is littered with examples of teachers who meant by those terms quite different ideas. Orthodox words are the passports of heretics that enable them to move freely, and without suspicion, among churches.
2. We should never be so naive as to think that false teachers wear disguises as authentic as a Groucho Marx "spectacles-nose-moustache" combo. False teaching never seeks to pass itself off as false teaching but as orthodox, sound, biblical, authentic, gospel truth. It is amazing that preachers can change their theology quite radically and yet in the same breath say that they have always believed the gospel. The less convincing the disguise the more likely it will be that a reaction will be caused, a controversy flare up, and maybe the progress of error will start to slow down.
Just like that little boy Edmund who got into so much trouble because of the taste of Turkish Delight we too are prone to theological temptations that are coated in sugar. But of course, like Edmund, we ought to recognise that the problem too is in our own sinful desires that heresies simply pander to. After all the serpent has told us that we can be like God knowing good and evil.