Be sure not to miss the comments of the post. Also, this post links to a previous discussion of 1Jn 2.23 (at that verse). The link, with its comments, discusses the longer reading of 1Jn.2.23 and 1Jn. 3.1. My position, on these two verses, is acceptance of the longer readings in both texts rather than the clauses being explanatory additions. The KJV misses these two important statements of scripture.
Evangelical Textual Criticism: FOMO, Missing Verses, and Helping Laypeople Think about Textual Criticism
beliefspeak2 