On the day of transition (Pentecost) from the Law to Grace, there must have been many of the people there that went their way and thought “it’s too simple, it can’t be real”. For some today the doctrine of Pentecost is too hard and they want to simplify that by taking away from the word of God. The oversimplified “gospel” of many churches does not produce the results they want, but it will produce results they don’t want.
But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
For do I now persuade men, or God? or do I seek to please men? for if I yet pleased men, I should not be the servant of Christ.
John wrote what was dictated by Jesus,
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.
It obviously doesn’t pay to fool around with the Word of God without permission. The penalties are rather severe.