This is the second shortest book in the Bible (III John is slightly shorter).
There was no question in the minds of the church fathers who lived closest to the time of John that these three epistles (I, II, and III John) were written by the apostle.
John wrote this perhaps to accompany his more general letter (I John). He may have hoped it would renew commitment to the truth by further exposing the false teachers.
This is a brief personal letter by the Apostle John to “the elect lady” (the church).
The book was written that we might know how to deal with heretics. John’s warning is stern, but he knew that a letter is not the best place to go into detail, so he promised to deal more fully with the problem when he would come for a personal visit.
It warns that people who do not hold to Bible teaching about Christ are not saved.
John commended love as a necessary ingredient of the Christian life, but it must be discerning. It must not blindly embrace those who willfully seek to destroy the truth.
It is false love that opens the door to false teaching. John even warned the people not to receive into their house anyone who rejected the teaching of Christ. Biblical love is a matter of choice; it is dangerous and foolish to float through life with undiscerning love.
All three of John’s letters develop the theme of fellowship:
I John focuses on fellowship with God.
II John focuses on fellowship with the enemies of truth.
II John focuses on fellowship with proclaimers of the truth.
John suggested in the book that truth without love produces dictatorial severity, but love without truth leads to blind sentimentality.