Since the early days of the church, people have tried to deny the Incarnation and still call themselves Christians. The little letter of 2 John is an answer to them and a reaffirmation of the truth about God in the flesh.
Because humans were dead in our sins, the only possible solution was for God to make us alive because of his grace.
Because God's power is greater than ours, we ought to obey God, knowing that the joy he gives is greater than suffering humans can...
Because Acts 25 shows us that things aren't always as they seem, we need to walk by faith and not by sight.