John called himself the elder. He may have been talking about his age or about being a church elder. He said he was writing to a lady and her children whom God chose. This was a way to talk about the church.
It was common for churches to meet in someone’s home. It was also common for believers in Roman lands to be treated badly for following Jesus. John may have avoided using any names to protect the believers.
John wrote that the truth is that Jesus Christ is the Son of God. He lived on earth as a human being with a human body. While Jesus was on earth he taught people how to live. People who follow Jesus’ teachings belong to God. They are part of God’s family together with everyone else who follows Jesus. That is why God’s children call one another brother and sister. They obey God’s commands. They lead a life of love like Jesus did.
John also wrote about the danger of lies and false teachings about Jesus. In John’s time, some people taught that Jesus didn’t ever have a human body. This teaching was based on a way of thinking called Docetism. These people thought that they knew many things and were proud of what they knew. John made it clear that people teaching these things didn’t follow Jesus’ teachings. They made themselves enemies of Christ. They didn’t lead a life of love. Instead, they did evil work. John warned the believers not to welcome such people. He meant that they weren't to be allowed to teach. John looked forward to visiting the believers and sharing his love and joy with them.