-This essay is meant to be read alongside the book it's about-
2 John is a very short single chapter letter sent by John the apostle which focuses on the concept of truth, its virtue, and its uncompromising and unchanging nature.
Verse 5 covers the unchanging nature of truth, it is something "which we have had from the beginning" and not something which was created at the time of this book's writing. The truth of Christ's doctrine is perrenial, it has always been the truth and always will be the truth. No amount of subjectivity, relativity, or anything can change the truth of Christ.
In verse 6 John declares that love should follow, he presents an imperative that we love one another. Love then is a product of practicing truth. If you abide or immerse yourself firmly in the fullest form of truth you will inevitably come to love one another because love is a manifestation of truth. Love is necessarily a selfless behavior, if selflessness is a manifestation of truth then you can reasonably conclude that the opposites of selflessness, personal pride and selfishness are not only sinful but are also untrue. The truth is that it is impossible to live up to the glory of God, so all pride is simply a falsehood which humans construct to obscure their need for Christ. Pride is wrong at both the moral level and the factual level.
Verses 7-8 describe a group of deceivers or "antichrists" who do not acknowledge the divinity of Christ, in John's time this would mostly be the Pharisees and Pagans. In modern times this would be Islam, Judaism, secular beliefs, and more.
Verses 9-11 discuss how to deal with these deceivers. Most of the threats John faced on this front are still present in modern society, the Pharisees are still infiltrating and deceiving Christianity to this day. Consider the phrase "judeo-christianity", which suggests a sort of spiritual alliance between Judaism and Christianity. While there may be some similarities between the religions they do not share the core perrenial truth of Christ and because of that they are incompatible. Everything that does not proclaim the divinity of Christ is deception according to John. Therefore, those who reject Christ in following the doctrine of Judaism are antichrists. John commands that those who don't bring the doctrine of Christ are to be rejected from our house nor should we even greet them "for he who greets him shares in his evil deeds." What this means is that we should not allow deceivers into positions of influence in the church, nor let them become influential in our social and personal lives. All you should give to these antichrists is the truth that is Christ's doctrine. Conservative christians often speak of a need to "bless" Israel and through deception they conclude that they need to do this through worldly means such as finance and politics. In reality the ultimate blessing is the truth of Christ, any other "blessing" you can offer is at best inferior or at worst is sharing in evil deeds. The jews rejected Christ and that makes them fundamentally incompatible with christians on spiritual matters. Why would they reject Christ? Because of the incentive to maintain a myth of racial superiority through their "chosen people" doctrine, the false doctrine of salvation and blessings being exclusive to the jewish people. That myth of racial superiority feeds a sense of pride and in them which creates a mindset of entitlement. Because pride is the most appealing and difficult sin to overcome you can see why these antichrists choose to spread deceptions and false teachings which favor their own interests, to pursue what worldly possessions and statuses they believe they are entitled to as a "chosen" race.
The ever increasing effectiveness of modern propaganda has resulted in many christians internalizing deceptions which by John's definition are absolutely the works of antichrists. The spiritual and worldly alliance that modern Christians have with Jews under the rhetoric of "Judeo-Christianity" is one of the most egregious acts of deception currently attacking the church, it has been internalized by an absurd amount of christians. Jesus and John were in a constant struggle with the Pharisees over their rejection of truth, yet the modern church often allies itself with the religious descendents of those same Pharisees, many sects of the modern church are falling for the same exact deception that John warned them of and are being exploited heavily as a result. Remember that everyone who rejects the doctrine of Christ is an antichrist who "does not have God." That includes conservative icons such as Ben Shapiro, who you should probably not listen to on several matters if you are to apply this scripture. "Do not receive him into your house nor greet him."
John takes a very absolute and uncompromising stance on truth. There is no room to entertain the ideas of someone who rejects the truth of Christ's doctrine. This absolutist stance can often be impractical and challenging to apply. You will have to make some sacrifices to maximally pursue truth, you may lose nonchristian friends, you will have to stop consuming nonchristian media, you will go through much struggle, but in doing so you will achieve something greater than anything you could have lost. Truth is always greater than untruth and an uncompromised truth is always greater than a compromised one. The optimal pursuit of truth will always consciously reject untruth, no matter how mundane. Only involve yourself with untruth as much as is necessary to understand it and consciously reject its influence.
The message of 2 John is one which helps us to understand just how sacred truth is and how dependent our spritual well-being is on the proper practice of truth. As well he shows how vital it is for us to reject deception at every level even if it is challenging to do so.