A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
2 John 1:1
jo2 1:1The elder--In a familiar letter John gives himself a less authoritative designation than "apostle"; so Pe1 5:1.
lady--BENGEL takes the Greek as a proper name Kyria, answering to the Hebrew "Martha." Being a person of influence, "deceivers" (Jo2 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 a warning to her. (But see my Introduction and Pe1 5:13). A particular Church, probably that at Babylon, was intended. "Church" is derived from Greek "Kuriake," akin to Kuria, or Kyria here; the latter word among the Romans and Athenians means the same as ecclesia, the term appropriated to designate the Church assembly.
love in the truth--Christian love rests on the Christian truth (Jo2 1:3, end). Not merely "I love in truth," but "I love in THE truth."
all--All Christians form one fellowship, rejoicing in the spiritual prosperity of one another. "The communion of love is as wide as the communion of faith" [ALFORD].
2 John 1:2
jo2 1:2For the truth's sake--joined with "I love," Jo2 1:1. "They who love in the truth, also love on account of the truth."
dwelleth in us, and shall be with us for ever--in consonance with Christ's promise.
2 John 1:3
jo2 1:3Grace be with you--One of the oldest manuscripts and several versions have "us" for you. The Greek is literally, "Grace shall be with us," that is, with both you and me. A prayer, however, is implied besides a confident affirmation.
grace . . . mercy . . . peace--"Grace" covers the sins of men; "mercy," their miseries. Grace must first do away with man's guilt before his misery can be relieved by mercy. Therefore grace stands before mercy. Peace is the result of both, and therefore stands third in order. Casting all our care on the Lord, with thanksgiving, maintains this peace.
the Lord--The oldest manuscripts and most of the oldest versions omit "the Lord." John never elsewhere uses this title in his Epistles, but "the Son of God."
in truth and love--The element or sphere in which alone grace, mercy, and peace, have place. He mentions truth in Jo2 1:4; love, in Jo2 1:5. Paul uses FAITH and love; for faith and truth are close akin.
2 John 1:4
jo2 1:4I found--probably in one of his missionary tours of superintendence. See Introduction, at the end, and Jo2 1:12; Jo3 1:10, Jo3 1:14.
of thy children--some.
in truth--that is, in the Gospel truth.
as--even as. "The Father's commandment" is the standard of "the truth."
2 John 1:5
jo2 1:5I beseech--rather (compare Note, see on Jo1 5:16), "I request thee," implying some degree of authority.
not . . . new commandment--It was old in that Christians heard it from the first in the Gospel preaching; new, in that the Gospel rested love on the new principle of filial imitation of God who first loved us, and gave Jesus to die for us; and also, in that love is now set forth with greater clearness than in the Old Testament dispensation. Love performs both tables of the law, and is the end of the law and the Gospel alike (compare Notes, see on Jo1 2:7-8).
that we--implying that he already had love, and urging her to join him in the same Christian grace. This verse seems to me to decide that a Church, not an individual lady, is meant. For a man to urge a woman ("THEE"; not thee and thy children) that he and she should love one another, is hardly like an apostolic precept, however pure may be the love enjoined; but all is clear if "the lady" represent a Church.
2 John 1:6
jo2 1:6"Love is the fulfilling of the law" (Rom 13:10), and the fulfilling of the law is the sure test of love.
This is the commandment--Greek, "The commandment is this," namely, love, in which all God's other commandments are summed up.
2 John 1:7
jo2 1:7As love and truth go hand in hand (Jo2 1:3-4), he feels it needful to give warning against teachers of untruth.
For--giving the reason why he dwelt on truth and on love, which manifests itself in keeping God's commandments (Jo2 1:6).
many-- (Jo1 2:18; Jo1 4:1).
are entered--The oldest manuscripts read, "have gone forth," namely, from us.
confess not . . . Jesus . . . in the flesh--the token of Antichrist.
is come--Greek, "coming." He who denies Christ's coming in the flesh, denies the possibility of the incarnation; he who denies that he has come, denies its actuality. They denied the possibility of a Messiah's appearing, or coming, in the flesh [NEANDER]. I think the Greek present participle implies both the first and the second advent of Christ. He is often elsewhere called the Coming One (Greek), Mat 11:3; Heb 10:37. The denial of the reality of His manifestation in the flesh, at His first coming, and of His personal advent again, constitutes Antichrist. "The world turns away from God and Christ, busily intent upon its own husks; but to OPPOSE God and Christ is of the leaven of Satan" [BENGEL].
This is a, &c.--Greek, "This (such a one as has been just described) is the deceiver and the Antichrist." The many who in a degree fulfil the character, are forerunners of the final personal Antichrist, who shall concentrate in himself all the features of previous Antichristian systems.
2 John 1:8
jo2 1:8Look to yourselves--amidst the widespread prevalence of deception so many being led astray. So Christ's warning, Mat 24:4-5, Mat 24:24.
we lose not . . . we receive--The oldest manuscripts and versions read, "That YE lose not, but that YE receive."
which we have wrought--So one oldest manuscript reads. Other very old manuscripts, versions, and Fathers, read, "which YE have wrought." The we being seemingly the more difficult reading is less likely to have been a transcriber's alteration. Look that ye lose not the believing state of "truth and love," which WE (as God's workmen, Co2 6:1; Ti2 2:15) were the instruments of working in you.
a full reward--of grace not of debt. Fully consummated glory. If "which YE have wrought" be read with very old authorities, the reward meant is that of their "work (of faith) and labor of love." There are degrees of heavenly reward proportioned to the degrees of capability of receiving heavenly blessedness. Each vessel of glory hanging on Jesus shall be fully happy. But the larger the vessel, the greater will be its capacity for receiving heavenly bliss. He who with one pound made ten, received authority over ten cities. He who made five pounds received five cities; each according to his capacity of rule, and in proportion to his faithfulness. Compare Co1 15:41. "There is no half reward of the saints. It is either lost altogether, or received in full; in full communion with God" [BENGEL]. Still no service of minister or people shall fail to receive its reward.
2 John 1:9
jo2 1:9The loss (Jo2 1:8) meant is here explained: the not having God, which results from abiding not in the doctrine of Christ.
transgresseth--The oldest manuscripts and versions read, "Every one who takes the lead"; literally, "goes," or "leads on before"; compare Joh 10:4, "He goeth before them" (not the same Greek). Compare Jo3 1:9, "Loveth to have the pre-eminence."
hath not God-- (Jo1 2:23; Jo1 5:15). The second "of Christ" is omitted in the oldest manuscripts, but is understood in the sense.
He--emphatical: He and He alone.
2 John 1:10
jo2 1:10If there come any--as a teacher or brother. The Greek is indicative, not subjunctive; implying that such persons do actually come, and are sure to come; when any comes, as there will. True love is combined with hearty renunciation and separation from all that is false, whether persons or doctrines.
receive him not . . . neither bid him God speed--This is not said of those who were always aliens from the Church, but of those who wish to be esteemed brethren, and subvert the true doctrine [GROTIUS]. The greeting salutation forbidden in the case of such a one is that usual among Christian brethren in those days, not a mere formality, but a token of Christian brotherhood.
2 John 1:11
jo2 1:11By wishing a false brother or teacher "God (or 'good') speed," you imply that he is capable as such of good speed and joy (the literal meaning of the Greek), and that you wish him it while opposing Christ; so you identify yourself with "his evil deeds." The Greek of "partaker" is "having communion with." We cannot have communion with saints and with Antichrist at the same time. Here we see John's naturally fiery zeal directed to a right end. POLYCARP, the disciple of John, told contemporaries of IRENÃUS, who narrates the story on their authority, that on one occasion when John was about to bathe, and heard that Cerinthus, the heretic, was within, he retired with abhorrence, exclaiming, Surely the house will fall in ruins since the enemy of the truth is there.
2 John 1:12
jo2 1:12I would not write--A heart full of love pours itself out more freely face to face, than by letter.
paper--made of Egyptian papyrus. Pens were then reeds split.
ink--made of soot and water, thickened with gum. Parchment was used for the permanent manuscripts in which the Epistles were preserved. Writing tablets were used merely for temporary purposes, as our slates.
face to face--literally, "mouth to mouth."
full--Greek, "filled full." Your joy will be complete in hearing from me in person the joyful Gospel truths which I now defer communicating till I see you. On other occasions his writing the glad truths was for the same purpose.
2 John 1:13
jo2 1:13ALFORD confesses that the non-mention of the "lady" herself here seems rather to favor the hypothesis that a Church is meant.