Are the concepts of mortal sin and venial sin biblical?

from the old testament

• Sin is falling short of God’s glory. It is not wonder, then, that within the giving of the Laws to the Israelites, God frequently repeated, “I am the Lord your God,” as if reminding them of His holiness as the main reason for the laws He handed down. An example is Leviticus 18:4: “You shall follow my rules and keep my statutes and walk in them. I am the Lord your God. You shall therefore keep my statutes and my rules; if a person does them, he shall live by them: I am the Lord.”

from the new testament

• Everyone sins (regardless of whether or not they belong to a particular church) and that all sin violates God’s holiness. Paul writes, “None is righteous, no, not one” and “all have sinned and fall short of the glory of God” (Romans 3:10, 23). Sin is universal, and no person avoids guilt apart from Christ.
• Though Scripture contains several lists of sins, those lists consistently place so-called “big” and “small” sins together. For example, the book of Revelation names “the murderers and idolaters, and everyone who loves and practices falsehood” as outside the kingdom (Revelation 22:15). In this, big sins like murder are listed alongside “small” ones like a lie. This is because our relationship with God is not based on avoiding a particular class of sins but on the saving work of Jesus.
• Some sins have greater consequences, such as sexual sin (1 Corinthians 6:18) and sins that are carried out rather than just thought of (e.g., actually murdering or committing adultery have greater consequences than expressing anger or lusting) (Matthew 5:21–22, 27–28). Also, Luke 12:48 shows that one’s awareness of sinning also impacts the punishment for that sin. But sin as an overall affront to God’s holiness is the same.
• Salvation rests on what Christ has done, not on human obedience. Jesus came to save sinners, lived a sinless life, and died as a substitute so that all who trust in Him are forgiven and reconciled to God (John 3:16; Romans 5:8; 2 Corinthians 5:21). The issue, then, is not the size of one’s sins but whether one has been united to Christ through faith.
• Jesus did not just die for past sins but for every sin a believer will ever commit. Peter said, “He himself bore our sins in his body on the tree” (1 Peter 2:24). Paul added that “there is therefore now no condemnation for those who are in Christ Jesus” (Romans 8:1). Nothing can separate believers from God’s love (Romans 8:38–39), not even serious moral failure.
• Still, God’s grace does not excuse our sin. Paul warned believers not to “continue in sin that grace may abound” (Romans 6:1–2) but to walk by the Spirit so that sinful desires lose their power (Galatians 5:16). Christians are called to repent quickly, pursue holiness, and live in gratitude for the One who saved them.

implications for today

Hiding a sin doesn’t do away with it. That sin nobody knows about? God knows. That unethical desire that we’ve never told anyone about? God knows. That ungodly thought? God knows.

All of us have sinned against God, and He is aware of each and every one. Whether you’ve committed what Roman Catholicism would call a “mortal” or a “venial” sin, every person stands guilty before a holy and righteous Judge. The wonder of the gospel is that God did not leave us to face His eternal wrath. In love, He sent His Son, Jesus Christ, who lived the sinless life we failed to live and then died in our place, bearing the penalty our sins deserved (1 Peter 2:24). His resurrection proves that the debt is paid in full and that eternal life is offered freely to all who trust Him.

The world often shrugs off “small” sins as unimportant. They need to know that any sin is an affront to God’s holiness, and that’s why we all need Christ. Scripture says, “Everyone who calls on the name of the Lord will be saved” (Romans 10:13). The world needs to hear this message. Believers are the messengers. Who have you told about Christ today?