New Testament

1 John

First John is a pastoral writing to churches shaken by a split, when some who denied that Jesus is the Christ come in the flesh had gone out from them (, ). It gives the remaining believers tests of genuine faith, belief in the incarnate Son, obedience to God's commands and love for one another, so that they may know they have eternal life (). It belongs in the Bible because it ties right belief about Jesus, holy living and love together, and teaches that 'God is light' () and 'God is love' ().

Author: The writing is anonymous, but the author speaks as one of those who heard, saw and touched the Word of life (1:1–3). Early tradition ascribes it to the apostle John, and its language is very close to John's Gospel; some scholars instead attribute it to a disciple or leader within a circle that preserved John's teaching.
Audience: Believers, whom the author calls 'little children' and 'beloved', in a church or group of churches after a painful departure of members who held a false view of Christ (2:18–19). Tradition associates these churches with the region around Ephesus.
When: Most likely in the last decades of the first century, often placed around AD 85–100, probably after John's Gospel, though the order is debated.
Where: Not stated. Early tradition links John's later ministry with Ephesus in the province of Asia.
Genre: First John has no greeting, no named recipients and no closing greetings, so it reads more like a sermon or pastoral tract than a letter. Its style is simple in vocabulary but circles around a few themes, returning to light, truth, love, obedience and belief from new angles. Read it as a spiral rather than a straight line, and watch for its many contrasts: light and darkness, truth and lie, love and hate, children of God and children of the devil.

Shape of the book

The Word of Life and Walking in the Light · ch 1The author proclaims the eternal life he has seen and touched so readers may share fellowship with the Father and the Son, and since God is light, believers confess their sins rather than deny them.
Obedience, Love and the Antichrists · ch 2Jesus is the Advocate and atoning sacrifice, those who know Him keep His commands and love their brother, and those who left and deny that Jesus is the Christ show the spirit of antichrist.
Children of God · ch 3The Father's love makes believers His children, who will be like Christ when He appears, so they do not go on in sin but love in deed and truth, as Christ laid down His life for us.
Testing the Spirits and God Is Love · ch 4Every spirit that confesses Jesus Christ come in the flesh is from God, and since God is love and sent His Son as the atoning sacrifice, those born of God love one another.
Faith That Overcomes and Assurance · ch 5Faith that Jesus is the Son of God overcomes the world, God's testimony is that eternal life is in His Son, and believers can know they have life and pray with confidence.

Themes

Assurance of Eternal Life. The author writes 'so that you may know that you have eternal life' (). He gives tests by which believers can recognize genuine life: confessing Jesus as the Christ come in the flesh, keeping God's commands, and loving fellow believers. These marks are meant to reassure the faithful as well as expose the false.
God Is Light. God is light, and in Him there is no darkness at all (). Walking in the light does not mean sinlessness: if we say we have no sin, we deceive ourselves (), but if we confess our sins, He is faithful and just to forgive ().
God Is Love. God is love (, ), and His love was revealed in sending His one and only Son as the atoning sacrifice for our sins (). Love begins with God: we love because He first loved us (). Anyone who claims to love God while hating his brother is a liar ().
The Truth About Jesus. The deceivers denied that Jesus is the Christ () and would not confess Jesus Christ come in the flesh (). John insists that the Son came 'by water and blood' (), probably meaning His baptism and His death, against anyone who would separate the divine Christ from the human Jesus.
Abiding. The verb to remain or abide appears again and again: abiding in the Son and the Father (), God abiding in those who love (, ), and the anointing remaining in believers (). It describes a lasting relationship with God, not a passing experience.

Where Christ is

First John is centered on the person of Jesus: the Word of life who was with the Father and was seen and touched (), the righteous Advocate and atoning sacrifice (), and the Son of God who came in the flesh. The letter's final confession calls Him 'the true God and eternal life' (). Denying the Son means not having the Father ().

The Word of Life Made Visible. Fulfillment. The opening, 'That which was from the beginning' (), echoes and . The eternal life that was with the Father was revealed in a real human body that could be seen and touched. (; ; )
The Atoning Sacrifice. Type and fulfillment. Jesus is the atoning sacrifice for our sins, and not only ours but those of the whole world (; ). The word recalls the mercy seat and Day of Atonement, where sin was covered by blood (), and the blood of Jesus cleanses from all sin (). (; ; ; ; )
The Righteous Advocate. Fulfillment. When believers sin, they have an Advocate with the Father, Jesus Christ the Righteous (). The same Greek word is used in John's Gospel for the Spirit, 'another' Helper like Jesus (). (; ; ; )
The Son Who Destroys the Devil's Works. Promise and fulfillment. The Son of God appeared to destroy the works of the devil (), who has sinned from the beginning. This echoes the first promise that the woman's offspring would crush the serpent (). (; ; )

Voices

Augustine. In his homilies on 1 John he summed up the letter's ethic as 'love, and do what you will', meaning that when love for God and neighbor is the root, even correction and discipline will be done out of love rather than mere outward kindness or harshness. More from Augustine at CCEL ↗

Reading well, key terms and common misreadings

Read it well

Keep the church split in mind (2:19). Many of the strong statements are aimed at those who left and their teaching, and are meant to reassure those who stayed.
Read 1 John alongside John's Gospel. Light, life, truth, love, abiding and believing carry the same meanings, and John 20:31 and 1 John 5:13 state matching purposes.
Expect the same themes to return in different combinations. Tracing how belief, obedience and love interlock is the key to the letter.
Note a textual point at 5:7–8. A longer wording naming the Father, the Word and the Holy Spirit appears in the King James Version but is missing from the early Greek manuscripts, so modern translations like the BSB omit it.

Key terms

Fellowship κοινωνία (koinōnia) — Sharing a common life. The author's aim is that readers share fellowship with the apostles and with the Father and the Son (1:3), and walking in the light brings fellowship with one another (1:7).
Atoning sacrifice, propitiation ἱλασμός (hilasmos) — A sacrifice that deals with sin before God (2:2; 4:10). Translators differ between propitiation, stressing the turning away of God's wrath, and expiation, stressing the removal of sin; many think it includes both.
Abide, remain μένω (menō) — To stay or dwell. A favorite word of John's, describing the lasting union between believers and God (2:24, 2:28; 4:16).
Love ἀγάπη (agapē) — Self-giving love, defined by God's act of sending His Son (4:9–10) and shown in deed and truth, not only in words (3:18).
Antichrist ἀντίχριστος (antichristos) — One opposed to Christ or setting himself in Christ's place. The term appears in the Bible only in John's letters (2:18, 2:22; 4:3; 2 John 1:7), where John says many antichrists have already come, namely those who deny the Father and the Son.
Advocate παράκλητος (paraklētos) — One called alongside to help or plead a case. Used here of Jesus before the Father (2:1).

Easy to misread

Reading 3:6 and 3:9, the one born of God does not sin, as teaching that true believers never sin. John has already said that denying our sin is self-deception (1:8–10). The better reading: the present tense describes a settled pattern of life; believers do not go on living in sin as a way of life.
Turning the tests into a constant source of doubt. The tests are offered so that believers 'may know' they have eternal life (5:13), and John reassures those whose hearts condemn them that God is greater than our hearts (3:20).
Reducing 'God is love' to the idea that God approves of everything. John defines love by the atoning sacrifice of the Son (4:10) and by keeping God's commands (5:3), and he also says God is light (1:5).
Treating the sin that leads to death (5:16) as one specific, identifiable sin. Interpreters differ: some think of the deliberate rejection of Christ shown by those who left, others of persistent unrepentant sin. John does not name it, so caution is wise.

Further reading: David Guzik, Enduring Word · Matthew Henry on CCEL · BibleProject overview video