This verse gives the reason why John loves the congregation he is addressing. It is because the truth has been revealed to him and to them. Where the clause is preferably rendered as a new sentence, one may say therefore ‘this love is (or I love you) because of the truth which….’

Because of the truth which abides in us can be rendered as ‘because the truth abides in us,’ or ‘because it (referring to ‘truth’ in verse 1c) abides in us,’ or ‘because the truth constantly is with us (or among us).’ For “to abide in” see comments on 2.14. The personal pronoun “us” has inclusive force in this and the next clause. It refers to John, his readers, and “all who know the truth.”

And will be with us for ever is in the Greek a new sentence, but translators usually do as Revised Standard Version, taking it with the preceding sentence. The clause serves to reinforce and emphasize abides in us; the truth is and remains in us, and it will never stop doing so.

With us: this preposition is virtually synonymous with the one in the preceding “in us” (as is shown by 1 John 4.16 and 17, “with you—in you”). For for ever see comments on “eternal” in 1 John 1.2.

Quoted with permission from Haas, C., de Jonge, M. and Swellengrebel, J.L. A Handbook on The Second Letter of John. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .