It is difficult but not impossible to discover why the Epistle was written. There are three statements which at once describe the purpose of the Apostle in writing, and at the same time the object of the Christian life.
1. Fullness of Joy. — "These things we write that your joy may be full" (1:4). Joy is God's purpose for man, for sorrow originally came from sin. Our Lord's first miracle was wrought at a wedding; his second in a home ; thus we have, first, Christ and life's gladness; and only afterwards Christ and life's sadness. Joy is necessary for all true life (Neh. 8: 10). Even in education the influence of joy is undoubted, for young children are particularly responsive to a bright, buoyant, joyous teacher. Sorrow, while often made the instrument of discipline, may and sometimes does harden, but joy never hardens. We should, therefore, settle it in our minds that God intends us to have the fullness of joy.
2. Freedom from Sinning. — "These things write I unto you, that ye sin not" (2:1). This is another part of the Apostle's purpose. He wished and intended his readers not to sin. There is, as we shall see, a clear distinction between sin and sins, between root and fruit, principle and practise, and the Apostle, while carefully teaching that the principle of sin remains (1:8), is equally careful to teach that this root need not and should not produce fruit (2:1). But if there should be any sinning God has made provision in the Divine righteous Advocate (2:1, 2).
3. Spiritual Assurance. — 'These things have I written unto you, that ye may know that ye have eternal life" (5:13). Assurance means the consciousness of our position and relation to God. Faith possesses; assurance knows that it possesses. This idea associated with the word ''know" is in some respects the most prominent feature of the Epistle. "We know" is found fifteen times; "ye know" six times; "we have known" once; "ye have known" three times; "he that knoweth" once. The English word "know" stands for two separate and distinct Greek words, and when careful attention is paid to their usage the result is much spiritual illumination. One implies intuitive knowledge, that which comes from fact, the evidence of our senses, that which is independent of ourselves (1:2; 2:29. See John 1 : 33 ; 13:7; 8:55). The other indicates experimental knowledge, that which comes to us as the result of our personal testing and experience. Sometimes the present tense is used indicating the process of acquiring this experimental knowledge (2:3, 29; 3:24; 4:2; 5:2). At other times the perfect tense is found, indicating that which has been permanently acquired by experience (2:3; 3: 16).
These three passages, when put together, give the purpose both of the Epistle and of the Christian life. There is a close and intimate connection between them. We are to have the fullness of joy because of our freedom from sinning, and this, in turn, comes from spiritual assurance. Thus, assurance is the secret of freedom from sinning and of the fullness of joy.