1 John 2:24-25

See that what you have heard from the beginning remains in you. If it does, you also will remain in the Son and in the Father. And this is what he promised us—even eternal life.

(v24-25, NIV)

Here, the beginning refers to the beginning of their conversion and walk with Jesus. John is referring to what they had heard in the beginning of their new life in Christ. What they heard in the beginning was the gospel. They heard and received the word of life. With regards to what they heard in the beginning, John further encourages them to endure. These false teachers and antichrists John was just talking about are ones who did not remain with us. Those who do not remain prove to be those who were never really one of us. We should remain in the father and in the son.

Of further encouragement is the promise of eternal life. Eternal life is promised to true believers and followers of the Lord Jesus Christ. Jesus Christ paid the penalty for our sins and we receive his righteousness by imputation. As a result, we can now be ushered in as adopted sons and daughters. By grace through faith in him we can receive eternal life.