John Wesley 
The Witness of the Spirit [EPUB ebook] 

How many vain men, not understanding what they spake, neither whereof they affirmed, have wrested this Scripture to the great loss if not the destruction of their souls! How many have mistaken the voice of their own imagination for this witness of the Spirit of God, and thence idly presumed they were the children of God while they were doing the works of the devil! These are truly and properly enthusiasts; and, indeed, in the worst sense of the word. But with what difficulty are they convinced thereof, especially if they have drank deep into that spirit of error! All endeavours to bring them to the knowledge of themselves they will then account fighting against God; and that vehemence and impetuosity of spirit which they call “contending earnestly for the faith, ” sets them so far above all the usual methods of conviction that we may well say, “With men it is impossible.”