Back when people wrote letters, they did so for lots of reasons. They wanted to stay in contact with a loved one from whom they were separated (This was especially true in the days before there were phones, and later when people had phones but long-distance calls were expensive.). They also wrote to share news (This was especially true in the days before social media.). And, especially when it was one generation writing another, they wrote to pass on life lessons — that might well include a warning of potential dangers.
I think all of these would be reasons for John writing his letters. He certainly wants to stay in touch, he has things he wants to share and he definitely wants to pass on important truths that include warnings of potential danger.
The danger John is primarily concerned with is what we refer to today as Gnosticism. It’s probably helpful to think of Gnosticism as being something like a spiritual version of COVID-19. It was a (spiritual) virus. Its origins were unknown. It popped up in places in slightly differing variants. And it could be quite deadly.
The central thread of Gnosticism was its conviction that everything spiritual was good, and everything material was evil. Material didn’t simply include possessions as we tend to use the word — it was everything tangible. All created things were evil — from the planet they lived on to food they ate to the human body. As you might imagine, this had staggering implications. The Gnostics believed the world couldn’t have been created by God, and Jesus couldn’t have been a human. No creation, no incarnation.
John takes clear aim at this throughout 1 John (as well as in his gospel). He starts the letter with a clear rebuttal of any notion that Jesus was not flesh and blood. He tells us in no uncertain terms that what they had 1) heard, 2) seen, 3) looked at (as in pondered) and 4) touched — “this we proclaim” (v. 1). The Gnostics liked to speak of Jesus as a phantom or apparition of some kind, but the one who was personally there with Him won’t have any of that.
This is eyewitness testimony, but it’s not the kind where someone had a brief glimpse or quick look, and as a result is unsure or possibly mistaken in what they think they saw. John and his companions were with Jesus for three years. They knew what they had seen and experienced, and they weren’t going to allow disciples to be bullied into believing something less by people who weren’t there.
Twenty centuries later, John’s words continue to speak powerfully to disciples. Though Gnosticism has come and gone, it’s important that we understand that our faith today isn’t based on speculation or wishful thinking any more than it was in the time of John. Our faith is based on the historical and theological record of what His followers witnessed. Thousands of manuscripts and copies verify it. Historians like Will Durant and H. G. Wells affirm Jesus’ historicity. But perhaps most impressive: Multitudes of the disciples’ contemporaries — people who had lived when and where the recorded events happened — not only embraced the good news, many of them suffered and died for it.
John knew what he was talking about, and we can too.