Strong words from the Doctor on Matt. 7:21-23:
Our Lord is emphasizing that though they say `Lord, Lord’, and are fervent and zealous, it may be nothing but the flesh. Great enthusiasm in these things does not of necessity imply spirituality. The flesh may account for that; it can counterfeit almost everything. We can perhaps emphasize this point best by quoting something which was written by Robert Murray McCheyne. That man of God, when he merely entered the pulpit, caused people to break down and weep. People felt that he had come straight from an audience with God, and they were humbled by his very appearance. This is what he said in his diary one day: `Today, missed some fine opportunity of speaking a word for Christ. The Lord saw that I would have spoken as much for my own honour as for His, and therefore He shut my mouth. I see that a man cannot be a faithful, fervent minister until he preaches just for Christ’s sake, until he gives up trying to attract people to himself, and seeks to attract them to Christ. Lord’, he ends, `give me this.’ Robert Murray McCheyne there recognizes this terrible danger of doing things in the flesh and imagining that we are doing them for Christ’s sake…
In other words, a man may be able to point to great results such as healings and so on, and yet they may signify nothing. And we should not be surprised at this. Are we not learning more and more in these days about the powers that are innate in man even in a natural sense? There is such a thing as a natural gift of healing; there is a kind of natural, almost magical power in certain people. For instance the whole question of electricity in the human frame is most interesting. We are merely beginning to understand it. There are people such as water-diviners who possess certain curious gifts. Then there is the whole question of telepathy, transference of thought and extra-sensory perception. These things are just coming into our ken. As the result of such gifts and powers many can do marvellous and wondrous things, and yet not be Christian. The natural power of man can simulate the gifts of the Holy Spirit, up to a point. And, of course, we are reminded by Scripture that God, in His own inscrutable will, sometimes decides to give these powers to men who do not belong to Him in order to bring to pass His own purposes. He raises up men for His own particular purpose, but they themselves remain outside the kingdom. It was God who called and used the pagan Cyrus.
D. Martyn Lloyd-Jones, Studies in the Sermon on the Mount (Kindle Edition)