All passages of Scripture must be understood in context, but some by their nature require more contextualization than others. First John is one such book. Without an understanding of the errors it was written to refute, the necessary result will always be more error, or at the very least, more confusion.
That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, concerning the Word of life— the life was manifested, and we have seen, and bear witness, and declare to you that eternal life which was with the Father and was manifested to us—that which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ. And these things we write to you that your joy may be full (1 John 1:1-4).
What was the occasion of this letter? Those who were causing the problems in Ephesus were here characterized in three ways by the apostle John. They were false prophets (4:1), they were deceivers (2 Jn. 7), and lastly they are antichrists (2:18,22; 4:3, 2 Jn. 7). These false teachers had broken with the true church and had “gone out into the world” (4:1). This break showed that they were not really of the truth (2:19).
Those believers who had not gone with them were overcomers 4:4), but they were overcomers who had been unsettled by the battle and who were greatly in need of encouragement. This is the pastoral encouragement that John provides in this letter.
What were the characteristics of the lies they had to deal with? From the internal evidence of this letter, and from the external evidence we have about Ephesus in the first century, we can piece together a pretty good understanding of the heresy John was attacking. The false teachers had both a doctrinal problem (2:26) and an ethical/moral problem (3:7). The doctrinal problem was that they denied the incarnation of Jesus. The ethical problem was that they claimed to be able to be “in the light” while taking some kind of weak view of their sinfulness and sins. They were somehow above it all, more mature than to have to deal with boring ideas of sin.
As it happens, we know a good deal about this brand of heresy in Ephesus at this time. The leader of the opposition against the apostle John in Ephesus was a man named Cerinthus. He was a leader of an early Gnostic group, and the Gnosticism was characterized by two great features—the necessary impurity of matter and the supremacy of knowledge. The first led them to deny the incarnation, which is in effect the materialization of the eternal one. Their arrogance and pride over their “inside knowledge” led them to their lovelessness and their lawlessness. Hence, we see John attack the heresy of Cerinthus at every key point. Christ is the very Son of God. We must walk in love. We must keep God’s commandments.
The first four verses begin the epistle without preliminary introduction. First we have the relative clauses — John begins with that which was from the beginning. But the eternal came here, and was seen, heard, and touched. John himself had leaned back on the Lord at the Last Supper. Our message — the word of life — is the word about the Word. Put another way, the gospel is the preaching of Christ.
The second thing is the importance of testifying and preaching. The first verb testify refers to the authority of the witness. The second refers to the authority of one commissioned.
Then we have intertwined fellowship. The gospel is declared in such a way as it creates fellowship between those who speak and those who hear, provided that those who speak are in fellowship with both the Father and the Son. The fellowship John has in mind here is not simply human sociability. This is a religious fellowship based upon transcendent realities. The reality in question here is the nature and meaning of that transcendent reality that came to live with us, as witnessed by the incarnation of Christ.
And last is the fullness of joy. John writes so that their joy would be full. This is only possible if their joy is built on the right foundation. That foundation must be the truth — truth about God, truth in God, true fellowship with God, and consequently, true fellowship with the others who are faithful.
As we consider these issues, we must come to understand that theological subtleties matter. The false teachers here did not deny that Jesus was the Christ — Cerinthus taught that Jesus was the Christ from right after his baptism until right before his death. In contrast, John insists that Jesus, the incarnate God, passed through the water and the blood (5:6).