What is the sin that does not lead to death?

from the old testament

• The sin not unto death is not found in the Old Testament.

from the new testament

• For such a simple letter, 1 John is surprisingly difficult at times. This is because of both John’s rhetorical style and his reliance on his readers' background knowledge, which we don’t have. It’s best to interpret this passage based on what we know from the letter and use context to consider how 1 John 5:16 fits with the rest of the letter.
• The immediate context of 1 John 5:16 is 1 John 5:13–15, which grounds the confidence of prayer in the assurance of eternal life. As 1 John 5:16 is also about prayer, it’s likely a continuation of John’s point in 1 John 5:14–15. Additionally, the larger context of 1 John is that it is a letter to believers (1 John 2:12–14) who were adversely affected by some they thought were believers leaving the community (1 John 2:18–19). In addition to errors about Christ (1 John 4:2–3), they were apparently teaching the believers that sinning was either acceptable or not real, explaining John’s exhortations that they were all sinners (1 John 1:8, 10) and that sin meant they needed to repent (1 John 1:9), and that sin necessitated the costly payment of Jesus (1 John 2:1–2). Thus, John told them to obey Jesus (1 John 2:3–6) and to stop sinning (1 John 2:1; 3:6).
• With that background in mind, we can consider three major views of 1 John 5:16, which reads, “If anyone sees his brother committing a sin not leading to death, he shall ask, and God will give him life—to those who commit sins that do not lead to death. There is sin that leads to death; I do not say that one should pray for that.”
• First view—categories of sin. The Roman Catholic church categorizes sins as mortal (unforgivable) and venial (forgivable). In their system, when one commits a mortal sin, such as murder, one cannot be saved and is eternally lost. Conversely, if one commits a venial sin and repents of that sin to a priest, he or she will be saved when dying. This view must be rejected outright for a couple of reasons. First, Scripture does not teach that there are categories of sins. In fact, Revelation 21:8, also written by John, combines both liars and the cowardly with murderers, showing that all sin is damnable. Second, Scripture teaches that all sin can be forgiven (1 John 1:9), except for the blasphemy of the Spirit, a unique sin committed by the Pharisees when they said the Holy Spirit was Satan (cf. Matthew 12:31–32).
• Second view—physical death. The natural reading of 1 John 5:16 is spiritual death, but some propose that John meant physical death. Thus, this view holds that the sins that lead to death are those that either have the natural result of death or are judged by God with death (cf. 1 Corinthians 11:30). While plausible, as with the Catholic category view, it leaves the reader guessing which sins are meant. The passage is one of confidence (“he shall ask, and God will give him life”). Yet, if the “sin leading to death” is unknown, then there can be no such confidence. A second issue with the view is that it’s difficult to understand why John would tell them not to pray for those who are dying as a result of their sin.
• Third view—spiritual death and a contrast between believers and unbelievers. Unstated in the previous two views is that John referred to the same type of people, specifically “believers,” because John refers to someone seeing “his brother” sin. However, this third view notes that only the first part explicitly refers to “brothers.” The second part could easily be “false brothers.” Thus, the confidence of prayer is linked to seeing believers sinning. Spiritual death best fits the immediate context of John's discussion of eternal life and the larger context of writing to believers to obey. As they see other believers also disobeying, they are to pray for them, confident that God will keep them from sinning unto eternal death. This is in contrast to the false brothers who left the Christian community. John warns that prayers for them do not come with the same guarantee. John is thus not telling them not to pray for unbelievers but not to pray with the same expectation that God will save them. This view is strengthened by the fact that the only other time John mentions “death” in this letter is spiritual death (1 John 3:14).
• While no view is without difficulty, one should look for an answer that best fits the overall context of the letter and that doesn’t introduce undue speculation, such as unnamed categories of sin. John’s lack of clarity on the types of sin indicates that his point wasn’t about specific sins. Instead, based on the rest of the letter, we should understand 1 John 5:16 as an extension of his ongoing discussion about two groups of people: those who were sinning believers and those who had previously claimed to be part of the Christian community but had left and were teaching false doctrine about Christ.

implications for today

When you see a fellow Christian caught in sin, your first response shouldn’t be judgment, gossip, or writing them off—it should be prayer. John reminds us that believers still struggle with sin, but their sin does not mean they are beyond God’s grace or that Jesus has abandoned them. Instead of judging and thinking, “How could they call themselves a Christian and still do that?” ask, “How can I pray for God to work in their life?”

The reality is that we are called to take sin seriously without losing hope. You may have a friend who keeps falling into the same temptation, or you may be battling a sin that you thought you would have conquered by now. Don’t confuse struggling with sin with being beyond God's reach. Confess your sin, turn back to Christ, and keep walking in obedience—and help others do the same. God is able to use the prayers of other believers—and your own prayers—as part of the way He keeps His people faithful.

This is especially important in a culture where people are quick to either cancel someone for their failures or excuse sin altogether. The Bible gives us a better way: neither condemnation nor compromise. When someone is struggling, love them enough to care about their holiness and to pray for them. And when you are the one struggling, don’t hide from God or His people. Run toward Christ. You don’t have to figure out whether someone is truly saved or whether their sin has crossed some mysterious line. That isn’t your job. Your job is to pray, encourage, speak truth, and trust God with the results. Jesus is the One who saves and keeps His people—and He invites you to participate in that work through prayer!