John lays out the importance of truth in the first chapter of 1 John. We cannot proceed in our Christian experience without having the foundation of truth. And this permeates how we live, how we treat others, how we view God, and what kind of teaching we are willing to accept from someone claiming to have spiritual authority. John reassures his readers that because he was an eye witness of Jesus Christ, we can truth what he is saying. It is in line with what Christ said, did and taught. It is the truth, and we can measure ourselves and other teaching against that standard.