The Certainty of Eternal Life

1 John 5:10-11, "He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son. And this is the testimony: that God has given us eternal life, and this life is in His Son"

Cf use of Eternal Life and Everlasting Life in the Gospel of John