Problem: John writes, “The elder to the chosen lady and her children, whom I love in truth” (2 Jn. 1). Who was this “lady,” and why was he writing that he loved her? Did John have a romantic relationship with this woman?
Solution: No, John is not referring to a romantic relationship. After all, John not only writes that he loves “the chosen lady,” but “not I only, but also all who know the truth.” Clearly, all believers love this “chosen lady,” John cannot be writing to his girlfriend (!).
There are two possibilities as to who this chosen lady is:
OPTION #1: This figuratively refers to the entire church
Advocates of this view point out that the church is often metaphorically referred to as the “bride” of Christ (Eph. 5:29ff; Rev. 19:7; 21:2). Moreover, in the OT, Israel was referred to as the “daughter” of Jerusalem (Lam. 1:6, 15).
Therefore, John could be personifying this church as a woman, who is “chosen” (c.f. Eph. 1:4). Also, in verse 8, John uses the plural pronoun to speak about this lady (“Watch yourselves…”), and in verse 5, he writes, “love one another.” Both of these imperatives are in the plural—not the singular.
As to why John might use such a literary device, Barker suggests that John was writing to a church under persecution,
Such a veiled allusion may have been, as Dodd suggests, a device for shielding the identity of the community from adverse action by public officials who opposed the Christian community. If the letter fell into unfriendly hands, it would seem to be nothing more than a private message to a friend.
The Greek lacks the article for “chosen lady.” So a better translation might be “a chosen lady” because of its absence.
OPTION #2: This literally refers to an individual woman
Advocates of this view argue that we should take this verse at face value. Other letters in the NT are written to individual people (e.g. 1 & 2 Timothy, Titus, Philemon; 3 John). Therefore, this letter should be no different. Moreover, this view makes sense of John referring to the lady’s “sister” and her “children” (v.13). If the children are the church, then why are they mentioned separately from the “chosen lady” and her “sister”? Of course, this would make sense of the plural imperatives mentioned above. Since this lady had a family around her (v.13), John would no doubt write to her in plural imperatives (vv.5, 8).
 Hodges, Z. C. (1999). The Epistle of John: Walking in the Light of God’s Love (p. 251). Irving, TX: Grace Evangelical Society. Stott, J. R. W. (1988). The Letters of John: An Introduction and Commentary (Vol. 19, p. 204). Downers Grove, IL: InterVarsity Press.
 Barker, G. W. (1981). 2 John. In F. E. Gaebelein (Ed.), The Expositor’s Bible Commentary: Hebrews through Revelation (Vol. 12, p. 361). Grand Rapids, MI: Zondervan Publishing House.