The Letters of John
Tyndale New Testament Commentary
John's affection for the recipients of his letters is clear: 'They are his "dear children", his "dear friends",' as John Stott points out. He continues, '[John] longs to protect them from both error and evil, and to see them firmly established in faith, love and holiness. He has no new doctrine for them.
On the contrary, he appeals to them to remember what they already know, have and are. Whenever innovators trouble the church, and ridicule whatever is old or traditional, we need to hear and heed John's exhortation, to continue in what we have learnt and received, and to let it continue in us.'