The letters written by St. John, as with many other letters in the New Testament, were written to address various errors espoused by Christian communities. In order to counter these errors, he stresses many aspects which are essential to the Gospel message. There is an emphasis on the communion between God and man, including divine filiation as well as the role faith in Christ should play in the Christian life. Additionally, Christians must be careful to observe the commandments and love their neighbor. Finally, the Church must be on guard against deceivers who have not accepted the truth about Christ.
In the first letter, the reader is exhorted to abide in God (John 2:6). Each must know God to have a relationship with Him. God himself is described as light and those who walk in his light have the truth (John 1:6). Further, the way that we know him and that we are walking in the light is by keeping his commandments (2:3). Those who keep His word are perfected and will be filled with love. He reemphasizes this point in his second letter: that love is following the commandments (2 John 1:6). Not a sentimental love, but love that requires action for the good of the beloved. We must take special care to love our neighbors because “love is of God, and he who loves is born of God and knows God” (John 4:7). In the third, John reminds us that we are to serve our brethren, especially strangers (3 John 5).
This relationship between God and man leads toward eternal life. However, communion with God requires true faith in Christ as the Son of God (2:23). “Whoever confesses that Jesus is the Son of God, God abides in him, and he in God” (4:15). All throughout, the first letter stresses that faith in the redemptive work of Jesus is paramount. Every Christian must profess that Jesus is the Christ and the Son of God (John 5:1,5).
Communion with God and faith in Christ makes a Christian a child of God (John 3:1). This divine filiation is different than Christ’s natural filiation, but it is still astounding. This is not a mere extrinsic declaration, but a true purification of our nature so we may see God as He is (John 3:2). This is not only a privilege, but also a responsibility. It places in us the obligation to avoid sin and practice love of brother. “No one born of God commits sin; for God’s nature abides in him, and he cannot sin because he is born of God” (John 3:9).
Finally, each letter exhorts the reader to accept the teachings handed on from the Apostles and maintain fellowship with them (John 1:3). He warns that some will try to lead them astray from the truth (John 2:18). Each person should be careful not to lose “what you have worked for” because everyone who abides in true doctrine “has both the Father and the Son” (2 John 1:8-9). Finally, we must be careful to accept apostolic authority so we may keep the commandments and abide in the truth (3 John 9).
The Church is called to maintain the teachings handed on to her by the Apostles. She must remain vigilant to protect her teaching from the errors of false teachers. God is both love and truth. The truth is cold and sterile without love. At the same time, love without truth is confused and listless. Love and truth are perfectly united in the person of Jesus Christ, and He sets us free. This is the good news that the Church must protect.