Now it seems to me that such a statement must of necessity be wrong, because if you adopt that line of argument then you have nothing whatever to say to the cults. For whatever we may think about them, if our only test is that of experience, then the cults really do seem able to offer what is required. Yet we would not for a moment grant that they are right, or that the experience they claim is true, because the cults say that they do not believe the truth.
In other words, there must be an objective test for what we believe. Experience is not a test; a man may become very happy and live a much better life than he did before, though he believes something that is not true. Things which are not true in and of themselves may at first appear to do us good because, of course, the devil can turn himself into an angel of light: it is pathetic to notice the way in which people forget that teaching. We must never base our doctrines upon experience, but upon the truth. That is the main reason for not accepting this attitude of letting any man believe what he likes. The Scripture tells us to prove the truth. ‘Evil communications corrupt good manners,’ writes Paul, to the people in the church at Corinth. You must not say, he tells them in 1 Corinthians 15, that it is irrelevant whether a man believes in the resurrection or not. It does matter, and if men hold a wrong view, eventually it will lead to something wrong in their behaviour. Our duty, therefore, as Christian people is to discover, as far as we can, the teaching of the Scriptures. Obviously we do not do that in a controversial spirit, since controversy for its own sake is always the work of the devil. Remember, however, that the opposite to that is not to say, ‘Believe anything you like as long as it helps you.’ Rather it is to ‘search the Scriptures’. So it is our duty to discover, if we can, what we are told in Scripture about this important and vital matter of the method of sanctification and we do so now in terms of our Lord’s teaching at this point in the seventeenth chapter of John.*
*Lloyd-Jones, D. M. (2000). The assurance of our salvation : Exploring the depth of Jesus’ prayer for His own : Studies in John 17 (392–393). Wheaton, Ill.: Crossway Books.