The elder unto the elect lady and her children, whom I love in the truth; and not I only, but also all they that have known the truth;
The elder. In a familiar letter John gives himself a less authoritative designation than "apostle:" so 1 Peter 5:1.
Lady. Bengel takes kuria (G2959) as a proper name; the Hebrew 'Martha.' Being a person of influence, "deceivers" (2 John 1:7) were insinuating themselves into her family to seduce her and her children from the faith (Tirinus); whence John felt it necessary to write, warning her. (But see 'Introduction,' and 1 Peter 5:13.) A church, probably that at Babylon, was intended. 'Church' is derived from kuriakee (G2960), akin to kuria (G2959); which, among the Romans and Athenians, means ekkleesia (G1577) - the term appropriated to the church assembly.
Love in the truth. Christian love rests on the Christian truth (2 John 1:3, end). Not merely 'I love in truth,' but "I love in THE truth."
All - all Christians form one fellowship, rejoicing in one another's spiritual prosperity. 'The communion of love is as wide as the communion of faith' (Alford).