First we need to look at the fruit of someone’s life. For this we simply need a pair of eyes and some basic good judgement. Sadly, unbelievers are able to look at many of the false prophets of today and recognize them for what they are, while Christians are being deceived.
Secondly we need the Bible against which to measure the doctrine. We live in times of relativism where truth has become relative to culture, political expediency and profitability. But truth is not relative and changeable. It cannot be manipulated. Truth is absolute, just as a wall is either vertical or not and it’s trueness can be measured by a plumbline or a spirit level, so a man’s doctrine is either true or false and the measure is the plumbline of God’s Word (Amos 7:7-8)
But then we need a third tool called ‘discernment’. Unfortunately in the last thirty years Christianity has become very sensual and subjective and much error has crept in because it ‘felt’ right. This kind of subjectivity is very dangerous in the hands of those who are unskilled or immature and yet godly discernment remains an important tool to the true child of God. Sadly, many who have been burnt by the subjectivity and emotionalism of modern Christianity have over corrected resulting in a cold, heartless and intellectual form of Christianity.
If you watch a skilled craftsman you will notice tht he has developed a ‘feel’ for his craft. He can often ‘sense’ that something is not straight or square and will then apply the straightedge or square to confirm or refute his ‘feeling’. BUT he cannot go by his ‘gut feel’ alone. There are a few amusement places in California where gravity does not seem to operate and where water seemingly flows ‘uphill’. This is an illusion to fool one’s senses into believing something runs upill when, in fact, it is running downhill.
One of the realities about being a Christian is that we are led by the Holy Spirit. ‘For as many as are led by the Spirit of God, these are sons of God.’ (Romans 8:14) The problem is that most of us are so fleshly that we often think we are being led by the Spirit when we are actually being led by the flesh. Thus, discernment becomes an unreliable tool in the hands of the carnal of fleshly believer.
http://antonbosch.org/discerning-good-and-evil