The most important test is the conformity to scriptural teaching. “Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God.” How do I know that this is a scriptural test? All I know about Him, I put up to the test of Scripture. Indeed, you get exactly the same thing in the sixth verse of 1 John 4 where John says, speaking of himself and the other apostles, “We are of God: he that knoweth God heareth us; he that is not of God heareth not us. Hereby know we the spirit of truth, and the spirit of error.” The first thing to ask about a man who claims to be filled with the Spirit and to be an unusual teacher is, does his teaching conform to Scripture? Is it in conformity with the apostolic message? Does he base it all upon this Word? Is he willing to submit to it? That is the great test.
Another test is the readiness to listen to scriptural teaching; to abide by it is always a characteristic of the true prophet. You will find that the other man rather tends to dismiss it. “Ah yes,” he says,” But you are legalistic, you are just a theologian. I have experience, I have felt, and I have produced this and that.” The tendency is not to abide by the teaching of Scripture but to be almost contemptuous of it; that has always been the characteristic of those who have tended to go astray. Read the history of the Quakers, and you will find that such an attitude became a prominent feature—the inner light rather than the objective teaching of Scripture itself.
D. Martyn Lloyd-Jones, The Love of God, 23-24 (Republished in Life in Christ: Studies in 1 John)