John warned them of antichrists who would infiltrate the church with false teachings that deny Jesus is the Christ, the Son of God. Though they joined the congregation, they did not belong to the fellowship of believers because they did not personally accept Christ. We should not be discouraged or influenced when someone abandons their Christian walk.
Those who don't accept Jesus as the Son of God don't know God though they profess to. We must be alert to false teachings of our time and not be swayed by them. We must hold onto the truth that was planted in us that Jesus is the Son of God who died for us on the cross, was resurrected on the third day, ascended into heaven, and gives us eternal life. This apostle's creed in our hearts protects us from false teachings of the antichrists.
Lastly, we must continue in Christ, with real hope that Jesus will come again and find us doing what is right. Then, we can be confident and unashamed before Christ. We can't do this by our own strength, but only through relying on Jesus' righteousness and being guided by the Holy Spirit (27).
Application: Father, thank you for sending Jesus your Son to lead me to righteousness. Please help me to continue in Jesus.
One Word: Continue in Jesus, relying on his righteousness and Holy Spirit