The speaker opens this letter by identifying himself as "the elder." That's a little more helpful, though a name would have been nice.
He says he's writing to "the elect lady and her children." Sounds pretty fancy—we're guessing he's out to impress.
The elder says he loves the truth and he's really glad to know that the lady and her children are upholding the truth, too (i.e., they haven't given into the naysayers in the elder's community yet).
Again, he says he's not trying to tell her anything new, but that they should "love one another." Nope, nothing new to see here. Basically, love means following in God's footsteps and doing the things he says we should do. We've been there, done that.
The elder warns the lady that all kinds of liars are roaming around telling people the wrong stuff about Jesus. These guys are antichrists.
He tells her that she needs to be on guard. If she starts to believe the things they're saying, she'll lose everything—everything she's worked for spiritually, that is.
The elder warns her not to let any of these naysayers into her house. Showing basic hospitality, apparently, is a way of supporting evil.
There are all kinds of other things he needs to tell her, but he's not going to put them in writing right now. He'll visit soon and explain more in person.
He ends by saying that her nieces and nephews say hi. Hi!