This letter is attributed to the Apostle John. He speaks not from the authority of an apostle who has seen the risen Lord, as would be his right. Rather he speaks from the position of being an elder of the church. He sends this letter ahead, expecting to be there in person soon. However, John has urgency to exhort the church to whom he writes to avoid listening to a particular group of false teachers, who are apparently deceiving, and leading people away from obeying Jesus’ command to love one another. If they allow themselves to be deceived, it could result in them losing a portion of their reward at the judgement seat of Christ. John does not desire that. Rather, he desires that their joy be made full, and they receive rewards that endure forever.
That John sensed such urgency to warn this flock of believers to avoid falling into deception, so that they receive a full reward, demonstrates the extreme high importance John placed on living effectively in order to gain rewards in the judgement. He will condense the teaching from John 15, his own gospel about the ministry of Jesus, which shows the importance of abiding in the vine that is Christ by obeying His commands. John will emphasize most particularly the command to love one another.