1The elder, to the chosen lady and her children, whom I love in truth, and not I only, but also all those who know the truth, 2for the truth’s sake, which remains in us, and it will be with us forever: 3Grace, mercy, and peace will be with us, from God the Father and from the Lord Jesus Christ, the Son of the Father, in truth and love.
4I rejoice greatly that I have found some of your children walking in truth, even as we have been commanded by the Father. 5Now I beg you, dear lady, not as though I wrote to you a new commandment, but that which we had from the beginning, that we love one another. 6This is love, that we should walk according to his commandments. This is the commandment, even as you heard from the beginning, that you should walk in it.
7For many deceivers have gone out into the world, those who don’t confess that Jesus Christ came in the flesh. This is the deceiver and the Antichrist. 8Watch yourselves, that we don’t lose the things which we have accomplished, but that we receive a full reward. 9Whoever transgresses and doesn’t remain in the teaching of Christ doesn’t have God. He who remains in the teaching has both the Father and the Son. 10If anyone comes to you and doesn’t bring this teaching, don’t receive him into your house, and don’t welcome him, 11for he who welcomes him participates in his evil deeds.
12Having many things to write to you, I don’t want to do so with paper and ink, but I hope to come to you and to speak face to face, that our joy may be made full. 13The children of your chosen sister greet you. Amen.
10-11 The application of John’s warning is now detailed. This “if” may or may not be true. Not everyone who approached her would be a false teacher. She must be discerning. She is to examine that person and determine if they are in line with Christ’s teachings. If not, they are to be rejected.
The practice of churches in the first century was to meet in someone’s home. Likely, Lady Electa had a church group meeting in her home. She would likely house visiting ministers and provide for their needs. Her accepting someone into her home would be seen as endorsing their theology. That is the principle stated at the end.
Indorsing or supporting false teachers does not bring reward from Christ, but loss of reward. That is what John warned against in verse 8.