John now describes his purpose for writing along these lines. Verse 4 may perhaps stand for an introduction to the entire epistle. His primary purpose in this letter is to establish the hearts of God’s people with all the comforts that only genuine faith in Christ can produce. But he also intends to separate the sheep from the goats. He wants God’s people to observe the things that distinguish them from the carnal professor. Thus, he lays down a number of tests whereby we may “know that we know Him.” His aim is to shatter the false confidence of those who say they know God while walking in darkness, while establishing the comfort and joy of those who truly have an unction from the Holy One.

His epistle, then, is addressed to the true believers in Christ. He desires that they may walk in fullness of joy. He will point them in that direction by reminding them of the evidences whereby they may know that they truly are the children of God. Those who see that they do love the brethren, walk in the commandments of God, and have the abiding presence of the Spirit, can indeed rejoice with joy unspeakable and full of glory. John has no sympathy at all with the popish idea that no Christian can have true assurance of salvation. Fullness of joy can only come to those who are secure in the knowledge that they are Christ’s, and Christ is theirs. Those who genuinely are in saving relationship with the Saviour, John would have to walk above the doubts and fears to which believers are all too often subjected. They ought to have fullness of joy, because the joy of the Lord is our strength. Thus, the holy apostle states his purpose, and will quickly begin to explain the means whereby God’s children can attain to fullness of joy.