The denial is not that of a believer, he has eternal life. The denial is of a lost person who is still dead in trespasses and sins. Jesus bore the penalty for all of the sins of the world (1 John 2:2) and was even punished as sin in principle (2 Corinthians 5:21).
Condemnation remains not because of one's behavior, but one's denial of Jesus as their life-giving Savior. It’s just like Jesus told Nicodemus: “Whoever believes in Him is not condemned, but whoever does not believe stands condemned already because he has not believed in the name of God's one and only Son.” (John 3:18). If a person does not have eternal life, they remain condemned because they continue to reject Jesus.
When you trust Christ as Savior, He gives you eternal life (John 3). It’s eternal so it can never end. And it can’t end, because it’s Christ’s very own life. No human being can ever take that life away, including you or me (John 10:27-30). Even in a moment of weakness under torture, He will not abandon that person to hell. He is the Faithful One, not us. In fact God’s faithfulness through the Holy Spirit not only produces His fruit in us (Galatians 5:16-18, 22-26), He keeps us blameless, and brings peace to our hearts even when we fail Him:
“May God Himself, the God of peace, sanctify you through and through. May your whole spirit, soul and body be kept blameless at the coming of our Lord Jesus Christ. The one who calls you is faithful and He will do it.” 1 Thessalonians 5:23-24
Call on My name and confess all you have done. I will separate your sin from you and cast it away and remember it no more. ~ Jesus [Letters from God and His Christ - Volume 2 - Love and Forgiveness Awaits All Those Who Turn From the World to Christ]
