At the time John wrote this letter, there were many false teachers. The writings of Irenaeus (The Ante-Nicene Fathers, Volume I, Irenaeus Against Heresies, Book I, chapter XXIV, paragraph 4; chapter XXV, paragraph 4; chapter XXVI, paragraph 1) in the second century may provide a glimpse of the false doctrines that were being spread toward the close of the first century.
According to Irenaeus, Cerinthus, a contemporary of the apostle John, “represented Jesus as having not been born of a virgin, but as being the son of Joseph and Mary according to the ordinary course of human generation, while he nevertheless was more righteous, prudent, and wise than other men. Moreover, after his baptism, Christ descended upon him in the form of a dove from the Supreme Ruler, and that then he proclaimed the unknown Father, and performed miracles. But at last Christ departed from Jesus, and that then Jesus suffered and rose again, while Christ remained impassible, inasmuch as he was a spiritual being.”
Concerning a certain Basilides, who lived during this general period, Irenaeus said that he taught the following about Jesus: “…he did not himself suffer death, but Simon, a certain man of Cyrene, being compelled, bore the cross in his stead; so that this latter being transfigured by him, that he might be thought to be Jesus, was crucified, through ignorance and error, while Jesus himself received the form of Simon, and, standing by, laughed at them. For since he was an incorporeal power, and the Nous (mind) of the unborn father, he transfigured himself as he pleased, and thus ascended to him who had sent him, deriding them, inasmuch as he could not be laid hold of, and was invisible to all.”
The false teachers regarded themselves as possessing special enlightenment and as being superior to Christians generally. They looked down upon those not sharing their “deeper knowledge.” Basilides, for example, viewed one who believed that Jesus was put to death as being “still a slave.” Clearly, men such as these had no love for the genuine Christian brotherhood.
By reason of their claimed exalted spiritual state, certain ones contended that even the most atrocious deeds committed with their bodies had no bearing on what they were inside. They did not acknowledge the seriousness of sin. Irenaeus wrote regarding the followers of Carpocrates: “So unbridled is their madness, that they declare they have in their power all things which are irreligious and impious, and are at liberty to practice them; for they maintain that things are evil or good, simply in virtue of human opinion. They deem it necessary, therefore, that by means of transmigration from body to body, souls should have experience of every kind of life as well as every kind of action (unless, indeed, by a single incarnation, one may be able to prevent any need for others, by once for all, and with equal completeness, doing all those things which we dare not either speak or hear of, nay, which we must not even conceive in our thoughts, nor think credible, if any such thing is mooted among those persons who are our fellow-citizens).”
John’s letter filled a vital need, exposing the views of false teachers by setting forth the truth in an uncomplicated, straightforward manner. He developed the following points: Jesus Christ did indeed come in the flesh. A failure to show love for one’s brother proves that one is not enlightened but is walking in darkness. An inner change effected by God’s spirit is manifest in the purity of the outward life. It does matter how the fleshly body is used. A life of sin is incompatible with one’s having fellowship with the Father, his Son, and other children of God.