Unobservant readers may not have noticed that this passage was likely not originally included in John’s Gospel. Most translations today indicate this in some way. For many this could be something that would trigger doubts or uncertainty about the reliability of Scripture. The fact that this passage likely does not belong here strengthens our confidence in Scripture, however.
The New Testament is likely the most well attested ancient document in existence. Sure, we don’t have the originals, but we also don’t have original copies of most ancient writings. What we do have is thousands of ancient copies, some from near the actual dates of composition. So, the text that we have to read today, with all of the important variations and the couple likely add-ons, is something we can confidently believe was what was originally written.
So what do we do with a passage like this one that probably isn’t something John wrote? Most scholars contend that, even though it probably wasn’t a part of John’s Gospel, it was likely a historical event. Also, it agrees with the greater canonicity of the Gospel teaching, and doesn’t add any unique teaching not found elsewhere. A good approach may be, read it but don’t rely on it.
However, as is true of Scripture throughout history, this passage is especially helpful in today’s culture. It gives us a practical example of Jesus’ teaching regarding judgement. (That is probably why it most frequently was inserted here.) It harkens back to Jesus teaching in chapter 3 as well. Right after what used to be the most known verse in Scripture (3:16), we see that Jesus came to save the world, not judge it. And, those who believe in Him are spared from judgement, saved from sin. What we see from Jesus here is not a tolerance for sin, but a forgiving approach that still takes sin seriously. All sin, not just the most ostracized varieties. It is a sharp contrast to the new, most known and most misquoted verse of Scripture: Matthew 7:1.