Hebrews 6:1 Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God, 2 and of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment.
Eternal judgment is a very important foundational teaching for every believer to know and keep in the forefront of his thinking. Eternal is forever! The scriptures tell us that it is appointed for all people to die once and then face judgment - a judgment that is eternal Hebrew 9:27). Jesus taught us that the unrighteous go away to eternal punishment and the righteous go away upon death of their body to eternal life (Matthew 25:46). Who is righteous and who is unrighteous? What is the standard people are judged by? Who is the judge?
All people begin life unrighteous (Romans 3:10, 23). Every person is unrighteous no matter what good deeds they have done. All have sinned and it takes only one sin to fall short of being righteous (James 2:10). All people will experience eternal punishment in the Lake of Fire (Revelation 21:8) because all people have sinned and are unrighteous.
How does a person become righteous? A person becomes righteous by repenting of his sin and believing the gospel (Mark 1:15; 1 Corinthians 15:3-4; Romans 10:9); by exercising faith in Jesus (Romans 3:21-26)
The standard people are judged by is Law of God. If a person doesn't live according to all the ten commandments (Exodus 20:1-17) for his entire life, he does not meet the standard of righteousness required to enter life after being judged. The Law of God reveals sin but cannot save us from being condemned by sin (Romans 7:7,13; 8:1-4). If a person breaks the Law at one point, he has broken the entire law (James 2:10) and will experience the sentence of eternal torment at the final judgment.
The Creator God is the Judge (John 1:1-3; 8:16, 50). God is loving and God is just. He revealed His love and justice by dying on the cross for unrighteous man (Love - John 3:16; John 15:13; Justice - 1 Peter 3:18; Romans 5:12-21; Galatians 3:10).
One day all of us will experience judgment before God and the sentence is eternal. If we are unrighteous we will experience eternal punishment in the Lake of Fire (Revelation 20:11-15). If we are righteous we will experience eternal judgment resulting in life in the new heavens and earth (2 Corinthians 5:10; Revelations 21:1-4). Today we can determine how we will be judged by the Creator God at the final judgment. If repent of our sin and believe the gospel we will be judged righteous in Christ and experience eternal life. If during this life we reject Jesus and don't repent of our sin then we will be judged unrighteous and experience eternal punishment.
Acts 17:30-31 ...God...commands all people everywhere to repent. For He has set a day when He will judge the world with justice by the Man He has appointed. He has given proof of this to all men by raising Him from the dead."