2 & 3 John - Truth
Early church tradition testified that 2 and 3 John were written by John the disciple of Jesus, who used a different title and called himself an “elder” in these two epistles (2 John 1:1). False teachers had infiltrated the church and taught that Jesus was not truly a man but only appeared to be one. Therefore, in these two epistles, John focuses on protecting our fellowship from those who teach falsehood. The apostle went so far as to warn his readers against inviting false teachers into the house or even offering them a greeting (2 John 1:10).
Testing the truth with God’s word
2 John 7 I say this because many deceivers, who do not acknowledge Jesus Christ as coming in the flesh, have gone out into the world. Any such person is the deceiver and the antichrist.
There will be many false teachers that will come and teach you something that deviates from the truth. The only way to detect these lies is to know the Bible well. In the example above, if someone comes to us with such a deviant teaching, we would reject it because the Bible teaches that Jesus came to us in the flesh.
John 1:14 The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the one and only Son, who came from the Father, full of grace and truth.
Losing the truth and our salvation
2 John 9 Anyone who runs ahead and does not continue in the teaching of Christ does not have God; whoever continues in the teaching has both the Father and the Son.
We are even in danger of losing our salvation if we drift so far from the truth that we no longer have genuine faith. This refers to losing our faith on issues that pertain to salvation. For example, losing our faith that God alone saves us by grace and being misled into believing that good deeds are necessary for salvation.
Avoid false teachings
2 John 10 If anyone comes to you and does not bring this teaching, do not take them into your house or welcome them.
John sees false teachings as so dangerous as to teach that we should avoid close fellowship with people who spread them. Although we should try to bring errant church members back to the right path, it is always dangerous to associate too closely with them because of the bad influence it may have on us.
Work to advance the truth
3 John 5 Dear friend, you are faithful in what you are doing for the brothers and sisters, even though they are strangers to you... 8 We ought therefore to show hospitality to such people so that we may work together for the truth.
While John warns against associating with people who spread false teachings, he encourages us to network with people that we can work together with to advance the truth.