John’s epistles are the only place in the Bible where the term “Antichrist” is used. And what that term—usually thought of more in relation to the beast of Revelation and Paul’s “man of lawlessness”—means here is eye-opening. Here the term is used for those who have claimed to be believers but who have abandoned the faith and apostolic teaching in favor of other ideas. The fact that these three instances here and one in 2 John are the only uses of the term is important to our understanding of the concept. We should not limit the idea of antichrist to the “Big Bad” at the end of time. John implies that the church age is full of them.
There is a lot of variety in Christian teaching. Ever since Luther opened the door in western Christianity for people to rely solely on Scripture for doctrine, people have been disagreeing on how it should be read. However, what Luther did was a correction on a large scale of the whole church turning away from sound doctrine.
Since then there has largely been agreement in reformed thinking regarding orthodoxy. Most of the variation in church teaching has either centered around minor, secondary doctrines, or has amounted to people taking different approaches to how orthodox teaching is lived out. Teachings that diverge beyond this tend to not line up with Scripture anymore.
What we want to avoid and guard against is the temptation to find new teaching, new ways of interpreting Scripture that have never been seen. That is the path towards dangerous, heretical, cultic leaning. The way of antichrists, is what John would say.
The other, even more sobering implication here is that the antichrist “spirit” arises out of—though never truly from within—the church. Other passages of Scripture, speaking of these bringers of false teaching, talk about how portions of the faithful will be deceived. The false teachings Scripture warns us against may not seem to be obvious, evil doctrines but rather appealing, seemingly spiritual ones. So, John’s exhortation here to “keep the faith” is of great importance!