‘The elder to the elect lady and her children, whom I love in truth, and not I only, but also all they who know the truth, for the truth's sake which abides in us, and it will be with us for ever.'
This verse is full of ‘truth'. He assures the recipients that his love for them is true, and that so is that of all who know the truth. This latter would suggest that ‘truth' therefore includes the fact that the recipients too love the truth. They love them because of the truth which abides within all of them, and will be with them for ever.
There may also be in this an indirect reference to the Spirit of truth (John 14:17; John 15:26; John 16:13) and the ‘anointing' that is within them (1 John 2:20; 1 John 2:27).
The emphasis here is that the true people of God need to preserve and live in the truth, because there are false teachers about, and that they should rejoice in being people of the truth, and in the confidence that they will indeed be so for ever. Thus there is the strong suggestion of their need to ensure that they remain in the truth, and not be led astray.