John writes the purpose of his first epistle in 1 John 5:13 "These things I write unto you that you may know that you have eternal life." John also states other purposes for his letter. He writes so that they would have fullness of joy (1:4), that they would not sin (2:1), and that they would not be seduced by false teachers (2:27).

The aged apostle John writes this little epistle from a pastor’s heart who has a concern for his people. He wants to make sure that they have genuine saving faith, and that they are not being swept away by the dangerous heresy of the day which was called Gnosticism.

It has been said that John writes with "a warm, conversational, and above all, loving tone, like a father having a tender, intimate conversation with his children." In fact, the word love is mentioned 33 times in this epistle.

John also tackles, in this short epistle, such things as false prophets, antichrists, loving the world, the second coming, idolatry, loving God, loving the brethren, prayer and much more.