1 John 5:13, “13 I write these things to you who believe in the name of the Son of God, that you may know that you have eternal life.”
The Early Church Fathers help Christians today to know about the Post-Apostolic Age of the Church. These men of the Early Church tell several stories about the later years of the Apostle John. One of these stories tells about John’s unwillingness to be in the same Ephesian bathhouse with Cerinthus, a false teacher. When Cerinthus entered the bathhouse according to these men, John fled, warning people, the Lord might cause the walls of the building to collapse in judgment on the heretic.
While this story, may or may not be true, even so, it’s clear from the earliest church history that Cerinthus taught false teaching that troubled many Christians. Cerinthus denied the Incarnation of the Son of God and taught that the spirit of the divine Christ came upon Jesus, the man at His baptism and left Him shortly before His death. This is one of the many varieties of docetism that plagued the early church and threatened biblical orthodoxy pertaining to the full deity and full humanity of the Lord Jesus Christ.
Cerinthianism may be one of the many reasons why John wrote 1 John. Either way, it’s clear that some people were concerning to John’s audience with their denials of the Incarnation. John throughout this epistle has repeatedly taught that the Divine Son Jesus became Incarnate as Jesus of Nazareth (1 John 5:6-12). With these affirmations, John is refuting the false teaching then current in the church.
The primary purpose as 1 John 5:13 tells us, was for John not only to refute false teachers but to impart the assurance of eternal life on those who held to biblical orthodoxy. Some Christians had been troubled by false teaching which resulted in doubts about their salvation, even as they had resisted heresy (1 John 2:19). John wrote to faithful biblical orthodoxy Christians to reassure them of their Christian faith. Even today, we may doubt, but as 1 John 5:13 tells us, the Lord God wants true Christians to know they have eternal life. When real Christians love God’s people, obey God, and confess the Incarnation, they can be sure they are born of the Holy Spirit (1 John 5:1-5)
Today, many theological traditions deny people the assurance of eternal life. Roman Catholicism denies absolute assurance is possible except for the greatest saints of the Church. John wants his Christian readers to know for sure they have eternal life. To do that, we merely need to ask and answer these questions in the affirmative, “Do you love fellow Christians? Do you aim to obey the Word of God daily? Do you confess the Incarnation of Jesus?” If you answered yes to those questions and lack assurance, please ask the Holy Spirit to testify clearly with these biblical truths so you can know beyond a doubt you are a real child and friend of God.