John 5:24 teaches that we have everlasting life now, in the present. Therefore, by definition, since it lasts forever, it cannot be taken away from us, otherwise God is a liar. And we know that God cannot lie!

John 5:24: "Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life."

From the sermon, "John 3:16", preached by Afshin Yaghtin: https://www.youtube.com/watch?v=jTKI2LAnHcg