The author of 1 John is the same John who wrote the gospel of John, the book of Revelation, 2 John, and 3 John. His letter was written so that true believers might know they have eternal life. The theme of the book of 1 John is not simply a discourse on the truth, but an exhortation to believe the truth and walk in it!
John clearly and firmly repudiates the lie that a believer does not need to look like His Father. Sons are supposed to look like their fathers because it brings glory to the father. In this day and age of independence and rebellion, the purpose of families is often forgotten. God established families in order to show us a picture of Who He is and what He expects from us. If we are saved, we are born of God; and if we are born of God, we are to resemble Him as closely as possible. This resemblance shows the world Who God really is and brings Him Glory!