1John5：16 If anyone sees his brother commit a sin that does not lead to death, he should pray and God will give him life. I refer to those whose sin does not lead to death. There is a sin that leads to death. I am not saying that he should pray about that.
That is an excellent question! So good, in fact, I had to grab a Study Bible to find the answer!
This is from 1 John 5:16-17 MacArthur Study Bible
NKJV MacArthur Study Bible
1 John 5:16, 17 John illustrates praying according to God’s will with the specific example of the “sin leading to death.” Such a sin could be any premeditated and unconfessed sin that causes the Lord to determine to end a believer’s life. It is not one particular sin like homosexuality or lying, but whatever sin is the final one in the tolerance of God. Failure to repent of and forsake sin may eventually lead to physical death as a judgment of God (Acts 5:1–11; 1 Cor. 5:5; 11:30). No intercessory prayer will be effective for those who have committed such deliberate high-handed sin, i.e., God’s discipline with physical death is inevitable in such cases as He seeks to preserve the purity of His church (see notes on 1 Cor. 5:5–7). The contrast to the phrase “there is sin leading to death” with “there is sin not leading to death” signifies that the writer distinguishes between sins that may lead to physical death and those that do not. That is not to identify a certain kind of mortal or non-mortal sin, but to say not all sins are so judged by God.
i think some sin does not so serious to leave God. However, if some sin is very serious, they will lead to death.
Amen, thank you for your answers, and for being so attentive to other people’s problems.God bless you.