My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous.
The audience is "my little children." That is, the apostle John was an elder writing primarily, though not exclusively, to those younger than him. And since John was one of the first believers on Jesus, all members of his audience were necessarily younger than John in the faith.
But more than just a letter of the elder to his little children (John calls himself "the elder" in II and III John), as the inspired Word this letter should be taken as direct from God the Father to His little children. Everyone who believes that the Word is inspired understands that this is the Father's letter to His children. That is, it is written to born-again believers and not to mere professors in the church.
So the fear that God intends to instill in His children is godly fear and not the ungodly kind. Ungodly fear is for those on whom the wrath of God still abides, cf. Jn 3:36. Ungodly fear is for all lawbreakers who haven't had their lawbreaking covered by the blood of Jesus. And such were formerly we.
But after we believed, ungodly fear is no longer our motive for worship or service. "There is no fear in love; but perfect love casteth out fear: because fear hath torment. He that feareth is not made perfect in love." I Jn. 4:18. As little children, it is godly fear that is now our motive for service.
I fully believe that the book of I John is the end of New Testament doctrine. That is, all the teachings in the New Testament are given so that each of us may walk with Him in blessed fellowship. The church epistles are given to this end also. The church is given by God for the edification of the saints. These edified and encouraged saints are then to go out into the world and live a life that is our spiritual worship, Rom. 12:1-2. First and foremost we are to preach the gospel. (It is not so much that the gospel is preached "in the church" but rather that the church, i.e., the individual members, go out and preach the gospel in the world.)
So the church is given for the edification of the saints, and each of these edified saints is to walk with God. Now we are back in the book of I John. You notice that I John is not a church epistle but a general epistle, that is, it is addressed to all the saints; in this case we are called little children. Further, I John is not only about walking with God but knowing we are walking with Him. "And hereby we do know that we know him, if we keep his commandments." I Jn. 2:3. The test is obedience to His Word.
So we are to understand that the book of I John is not for testing our salvation but for testing our fellowship with the Lord. It makes all the difference in the world that we understand this, for then our motivation for service is godly fear and not the other kind.
Any teacher who uses (or abuses, I should say) the book of I John in order to instill a fear of losing one's salvation, is a false teacher and a cult leader. By contrast, a sound teacher of the Word will indeed teach the book in such a way as to instill godly fear in God's little children.
There are other New Testament passages which concern the necessity for self-examination in order that we may each of us ensure that we are in the faith, that is, truly saved by the blood of Jesus. For example, Paul wrote,
"Examine yourselves, whether ye be in the faith." II Cor. 13:5a. And the entire book of Hebrews serves as a warning to members of the professing church that we may enter the visible church without having entered the invisible church through faith in Jesus. In this event the professors are like Israel that perished in the wilderness without entering into His rest in Canaan. They had God, they had the ordinances, and they perished. So is it true for many in the visible church.
But a person's standing before God is not the issue in I John, it is a believer's state or experience. A believer is already in right standing with God. The first and foremost thing to understand about I John is that it is addressed to the saints, or born-again believers, members of the one, true, spiritual, invisible, eternal church of Jesus Christ–the little children–and not to anyone who has merely confessed the Lord Jesus but never believed in his heart that God raised Him from the dead.
I am happy to believe and know that I am one of God's little children. And I hope to grow more childlike in my faith, more obedient in my service.