The Word of Life: 1 John 1:1-4
John begins his letter with numerous references to the fact that he himself was present for the entire story of what Jesus had done and taught. John was an eyewitness. His opponents, false teachers in the churches he was serving, were convincing people that even though John was an eyewitness, yet he did not know what was really happening or what it really meant.
John is going to address each of their claims over the course of this letter, among other things. But here at the beginning, he simply wants to remind them of key features of the Gospel: that we can have real fellowship with the real God by believing the real Gospel enacted and explained by Christ, and witnessed and recorded by those who were really there.