v1-4: The reality of Jesus Christ; the Word of life, that eternal life, the Son of God. Seen and heard by men; and seen and heard by "us," John and others. John was an eye-witness to the life of Christ (John 19.35). His experience, and that of the others with him, gives him authority to speak these things of Christ.

Jesus Christ was visible, audible, tangible; God manifested on the earth. The eternal word was manifested to us, as word became flesh.

John wrote to bring joy (v4), to encourage Christians, helping them to cope with the ordinary trials of life. Such fullness of joy comes through knowing God in Christ. We enjoy fellowship with God and with each other; here is the purpose of the gospel, and Christ's blood was shed to ensure this (v7).

He exposed the Gnostic heresy, with his three tests of faith;

• right behaviour, answering the view that a believer can live how he likes (anti-nomianism);
• right belief; answering attacks on the person of Christ;
• right brotherhood; answering claims of spiritual pride and exclusivity.

There are indications that John was a Levite, see John 18.15-16. He was therefore familiar with the priestly offerings. In the Burnt Offering, the skin was removed to ensure the inside was pure; in Lev 1.3, the animal was brought first to the priest to check it was without defect, "we have looked upon," or scrutinised. In the Grain Offering the priest took handfuls of the flow, "our hands have touched (handled)." John's conclusion, as the priest, was that this One was without fault, the perfect Son of God. This approach may also explain why the letter opens impersonally ("that which.."), referring to Christ as the perfect sacrifice.

v5: Our message; from God; divine origin, not human invention.

First, God is light; perfect in righteousness and holiness, without fault, defect, or weakness; seen supremely and totally in Jesus Christ; that light has come into the world (John 3.19). In Him is no darkness, James 1.17; there is no failing in Father or Son.

"God is light" must precede "God is love." To declare one without the other is to be untrue to Scripture.

v6: Our lives must be consistent with the message, that we might adorn the doctrine of Christ.

If we walk in darkness, yet claiming to have fellowship with Him;

• we lie, we deny our claim to belong to God;
• we do not practice the truth, see 3.10.

v7: If we walk in the light,

• we enjoy fellowship with each other,
• and we enjoy continuous cleansing.

Thus, we promote fellowship with others, and our fellowship with God.

This is not only a reference to moral purity. To walk in the light means to walk in honesty with other Christians. That is a crucial element of John's teaching here (see note on v4). The Christian life is not an elitist private spirituality, but a genuine engagement with our brothers and sisters in Christ.

John draws on his understanding of the Levitical sacrifices. Here is the trespass (or guilt) offering (Lev 5), which covers our all-too-frequent falling short.

Christ is our example here, "as He is in the light." The phrase "as He" occurs throughout the letter; see 2.6; 3.2; 3.3; 3.7; 4.17. John is setting the very highest standards for our behaviour and attitudes.

v8: Do not claim perfection in character;

• we deceive ourselves;
• the truth is not in us.

Some claim to be without sin; such claims are clearly false. We must be aware that we fall short in our character as well as our actions.

v9: We must confess our sins, not cover them, Prov 28.13. To confess means 'to agree with God,' or 'to tell it as it is.' This balances any claim to be without sin; there is no shame in confessing sins, the shame is in denying them. Our examples here include the thief on the cross (Luke 23.41); the prodigal son (Luke 15.18); Nehemiah (Neh 9.33); Joshua in his words to Achan (Josh 7.19); but we are warned by Adam's failure to confess (Gen 3.12).

The promise here, based on God's faithfulness, is that He will forgive and cleanse, Rom 3.25-26; Heb 10.17. A Yoruba proverb says:  “If a man acknowledges his offence as a transgression, he will not spend a long time kneeling down.” John does not command nor invite a long and painful 'confession;' rather a simple, albeit genuine, admission before God.

This is the Sin Offering (contrast v7 above), where there is specific confession of a specific sin (Lev 4).

v10: Do not claim sinlessness in living;

• we make God to be a liar;
• and His word is not in us.

This links with 3.9, which is more to do with a settled habitual attitude of sin and rebellion against God.