I was preparing my lesson for this coming Sunday evening I came across something that peaked my interest. In looking at the cross-references for the Heidelberg Catechism's answer to question 53: "What do we believe about the Holy Spirit?" The cross-reference was for the proposition "First, that he is true and coeternal God with the Father and the Son," and was 1 John 5:7-8. These two verses were supposed to support that proposition, but when I look at my ESV all it said was "For there are three that testify: the Spirit and the water and the blood; and these three agree." Looking at that, I thought to myself that's not right... So, I looked at my King James and it read: "For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one." So, I thought to myself again: I wonder if there is some sort of textual variant there. I looked, and sure enough, there was, and it is one of the more famous ones at that.
After talking with Dr. James White, the founder of Alpha & Omega Ministries, I found out that this was known as the Comma Johanneum or Johannine Comma. After doing some research I found out that the phrase "in heaven, the Father, the Word, and the Holy Ghost: and these three are one... [a]nd there are three that bear witness in earth," was an insertion into the text that occurred somewhere around 1000 AD. If it occurred before that in the Greek texts, it was something akin to interpretational note written in the margin of 1 John. However, Erasmus, when writing the 3rd edition of the Textus Receptus (the standard Greek text for around 300 years afterwards), inserted the text because it was present in the manuscripts he was using. The Textus Receptus was then the text that was used to translate the King James Version. Later research showed that the unreliable nature of this insertion, so it was excluded from later Greek texts such as the Nestle-Aland Greek New Testament and, the one that I use, the United Bible Society Greek New Testament. These to later Greek Texts are the basis for the majority of the the modern translations such the New International Version, New American Standard Bible, and the English Standard Version (my bible of choice).