Revelation 22:18-19

(18) For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book: (19) And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.

Here is a solemn testimony, and of Christ himself, the faithful And true witness, and delivered in the most decisive manner possible that the adding to, or taking from the words of the prophecy contained in this book, shall bring on the utter ruin, and everlasting misery of any and everyone so offending. And the reason is very obvious. Christ is God's witness, and his own. He hath delivered the whole truths necessary to salvation. He hath confirmed it in all ages, by Prophets and Apostles, by miracles and signs, and, above all, by his death, resurrection, and return to glory, and by the sending down the gifts of the Holy Ghost. And in the hearts of his people he hath given yet further confirmation, by the regenerating and quickening influence of God the Spirit. So that, attested by such evidences, for any man to call those words of Christ in question, to prevent or mutilate, to gainsay or resist, cannot but bring down the just judgment of God. Lord! give grace to thy people, to receive with meekness thy engrafted word, and to esteem it more than their necessary food.