1 John 1:5-2:11

John wrote to a people who were struggling with false teachings and with divisions. They were dealing with a pervasive doctrine that taught the “unreality of Christ”—the separation of divinity and humanity, which was the exact opposite of Christ’s incarnation: God in the flesh.
This resulted in division, frustration, and pain among the membership. And to help them to fight it, John took the time to teach that, contrary to the false teachers’ doctrines, Jesus is real. This Jesus whom He described was not the Jesus these false teachers taught. And naturally, he knew that they would want to come to know this Jesus better. And that comes to the point of the book: that which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ. 4 And these things we write to you that your joy may be full. (1JN 1.3-4 (NKJV))
John introduces a concept: finding fellowship with God and with one another. And he’s not talking about a meal, but rather, something far deeper. But for them to be able to do that, they would need to know God and to know themselves.