John was keen that we can distinguish between truth and lies (1 John 2:18-29) and it is clear from 1 John 2:19 that the lies he was talking about (denying the Father and the Son) originated within the church. Heresy (‘belief or opinion contrary to orthodox religious (especially Christian) doctrine’) is not the same as unbelief; it is a ‘form of that faith that is held ultimately to be subversive or destructive, and thus indirectly leads to such unbelief. Unbelief is the outcome, but not the form, of heresy.’ (Alister McGrath, ‘Heresy’ P 33) Heresy is like a Trojan horse, smuggling untruth into the church, and John is keen that we are not led astray. (1 John 2:26)
Over the years, many heresies have been condemned as deviating from orthodoxy (accepted or authorised doctrines or beliefs). These (Gnosticism, Docetism, Arianism, Modalism, Pelagianism etc.) often focussed on trying to explain the nature of God. Heresies often arose because people either accepted Christ’s deity but could not accept His humanity or vice versa; some led to the idea that Christians worship three gods (a view still held by Muslims, for example.) Many of the analogies we use to explain the doctrine of the Trinity are actually heretical in some form or other! We have to be content to accept the limits of our understanding and to remain within the revelation of Scripture. A useful diagram shows us that often we cannot go beyond the obvious:
We may think that heresy is no longer relevant to us, but ‘what has been will be again, what has been done will be done again; there is nothing new under the sun.’ (Eccl 1:11) We need to understand that we have an enemy who tries to outwit us (2 Cor 2:11). We can be led astray when we want to fit our beliefs into our culture rather than being transformed by God (Rom 12:1-2), when we feel marginalised and try to embrace the broad path which leads to destruction (Matt 7:13-14) or when we try to accommodate other beliefs without standing up for truth. We need to understand that God has given us all we need to live by the truth and seek to allow that truth to define us and our behaviour in every way.