"Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the Lord your God which I command you." (Deuteronomy 4:2 KJV)
"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: 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." (Revelation 22:18-19)
We absolutely add to the Bible man-made commandments and traditions not expressly taught there. All churches are guilty of that sin. However, when we add words to explain the Bible, that is not forbidden here. In fact, it is encouraged by Nehemiah's example.
"So they read distinctly from the book, in the Law of God; and they gave the sense, and helped them to understand the reading." (Nehemiah 8:8)
Notice that Nehemiah's purpose was NOT to add vain traditions or rules made up by men, but to give the sense and help people understand. That requires additional words. The proper interpretation of any writing is called exegesis, explaining what it means. The wrong interpretation of scripture is called eisegesis, adding thoughts or ideas to the text that are simply not there. Adding appropriate words to clarify the meaning is called epexegesis, and is what every preacher ought to do every Sunday.
