What is the biblical basis between mortal and venial sins?Answer:
In regards to your question about the forgiveness of sin and the concept of mortal and venial sin, I have listed some verses below with a short explanation.
Confesson of sin to the Church:
Matt 16:18-19; 18:18 - If read literally, obviously Jesus gave Peter and the Church the power to bind and loose, which means they have the power to adjudicate spiritual matters. Peter shows us examples of this in Acts 1 when he chose the twelfth apostle; in Acts 5 when he chose to bind Ananias and Sapphira; in Acts 15 when he decides to loose the practice of circumcision, et al.
John 20:23 - If read literally, obviously, Jesus is giving the apostles the power to forgive sins through His name. Protestants don't like this, so they spiritualize the verse to make it refer to the gospel, but that is not what Jesus said. If he wanted to say that the gospel is what forgives sin, He would have done so. The Catholic Church takes Scripture at face value, for no one has the right to spiritualize a passage without direct authorization from God.
2 Cor 5:18 - If read literally, it is clear that Paul is saying that his and the apostle's ministry involves reconciling people to Christ, which according to the above passage, is getting them to confess their sins to God through the Church.
James 5:14-15 - If read literally, it is clear that the Church is called when someone is sick and near death. The presbyters lay hands on the person, pray to God, and the person's sins are forgiven. That's what the verse says. Protestants don't like this so they either ignore the passage or spiritualize it to refer to the gospel, as they do with John 20:23.
Acts 2:38 - This passage teaches that repentance and Baptism are necessary for the forgiveness of sins. Baptism is administered by the Church. The same truth is taught in Mark 16:16. Protestants don't like giving such power to Baptism, so they make Baptism a secondary issue, but these passages simply won't allow such an interpretation.
Acts 19:18 - This shows that the people confessed their sins to a higher authority, the same as John 20:23 or James 5:14-15.
Mortal and Venial Sin (or degrees of sin)
Matt 12:39-45 - This passage shows the degradation to which sin can lead. Jesus says in verse 45 that "the last state of the man is worse than the first," which means that the man is deeper in his sin presently than he was in the past. This shows degrees of sin and debauchery. The deeper one is in sin the harder it is to come out of it.
Matt 23:14-15 - These passages show that the degree of eternal punishment is based on the degree of the sin. The Pharisees will receive a greater damnation for greater sin. The same principle is in Luke 10:12.
Luke 12:47-48 - This passage teaches that there are degrees of sin, depending on the knowledge someone has. If someone knows what to do but refuses to do it, he has committed a greater sin, and will be punished with a greater punishment.
The same principle is in John 5:14
John 19:11 - Obviously, since Jesus says, "he who delivered me up to you has the greater sin," this verse teaches that there are degrees of sin.
Acts 5:3-5 - Obviously, Ananias and Sapphira committed a horrible sin, and that is why their lives were taken. If they had just committed some minor offense (e.g., if they lied about Sapphira's age) they wouldn't have been killed. This again shows degrees of sin.
1 Cor 3:13-17 - Obviously, although the man of verse 15 is punished for his bad works, but he is still saved. But the man of verse 17 is "destroyed" for his bad works, and he is not saved. The latter sin is mortal, the former is venial.
1 Cor 6:9 - Paul is listing the major sins against the ten commandments. These will keep one from the kingdom of heaven. The same kinds of sin and eternal damnation is listed in Gal 5:19-21 and Eph 5:5. Obviously, these kinds of sin are different than the sin in 1 Cor 3:15 (noted above) in which the man who sinned venially can still be saved by fire.
1 Thess 2:16 - Again, there is a greater punishment for greater sin, since Paul says that "wrath has come upon them to the uttermost."
2 Tim 3:6 - This again shows the degree of sin. The men have a "form of godliness" but are the worst type of sinners underneath. They are like the Pharisees who will receive the greater damnation for greater sin (Matt 23:14-15).
Hebrews 10:26-30 - This shows that willful and deliberate sin removes one from the sacrificial power of Christ. That is mortal sin, the opposite of the person in 1 Cor. 3:15. Hebrews 10:29 says such a person will receive a "much severer punishment" because he has despised the blood of the covenant.
James 3:1 - This passage shows that a person who is in leadership is held to a stricter standard, and he will be judged accordingly if he sins.
1 John 5:16-17 - Obviously, this passage distinguishes between two kinds of sin: (a) that not leading to death, and (b) that leading to death. Death is mortal, and thus the Church calls such sin "mortal sin." If you want to call it something else, fine, but the point remains that there is a distinction between two kinds of sin. The one is so grievous that the people are told not to pray for the person (the assumption is that he has died in this sin).
Numbers 15:27-36 - The concept of degrees of sin and ignorance is not a new idea. It was first taught in the OT. This passage, and others like it in the OT, give a whole list of various levels of sin and culpability.
Deut 22:22 - This passage shows that capital crimes, such as adultery or murder, were serious sins that received the sentence of death. For minor sins, the person was required to pay a fine, which is the same idea in 1 Cor 3:15. In fact, the phrase "suffer loss" in 1 Cor 3:15 is derived from the Greek word for "fine, penalty, punishment."
Deut 29:19-21 - This passage shows that for serious and deliberate rebellion against God, God will no longer be willing to forgive. This is the same principle noted in Hebrews 10:26-29 or Hebrews 6:1-6.
I hope this helps you. May God give you much wisdom.
Catholic Apologetics International
July 16, 2001