“If anyone sees his brother sinning a sin which does not lead to death, he will ask, and He will give him life for those who commit sin not leading to death. There is sin leading to death. I do not say that he should pray about that.”
which does not lead to death,
The idea of “death” here is not spiritual death but physical death. Some Christians die prematurely because of protracted unconfessed sin (1 Co 5:5; 11:30).
Some Christians die physically before their time.
Christians begin eternal life at the point of salvation and can never lose that salvation at any future point.
Jn 10: 28 “And I give them eternal life, and they shall never perish; neither shall anyone snatch them out of My hand. 29 “My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of My Father’s hand.”
Jn 17: 11 “Now I am no longer in the world, but these are in the world, and I come to You. Holy Father, keep through Your name those whom You have given Me, that they may be one as We are.”
However, Christians can lose the experience of abundant living. They can blunt the modus vivendi of their spirituality.
Jn 10: 10 “The thief does not come except to steal, and to kill, and to destroy. I have come that they may have life, and that they may have it more abundantly.”
Christians also have the possibility of committing a sin to the point of corporal death. God sometimes signs the death warrant of Christians in intransigent sin. There are a number of occasions of the “sin unto death” in the Word of God. Ananias and Sapphira are cases in point (Acts 5:1-11). God sentenced them to death for misrepresentation of the facts. Paul assigned a Christian living in incest to death should he not repent (1 Co 5:1-5).
Moses committed the sin unto death by striking the rock (Nu 20:8, 12). Achan committed the sin unto death by hiding condemned garments in the book of Joshua. He and his family were put to death for this.
We should not confuse the “sin unto death” with the unpardonable sin. Only unbelievers can commit the unpardonable sin and only unbelievers of Jesus’ day at that. These are two different situations altogether. The unpardonable sin was the sin of attributing the work of Christ to the work of Satan.
Many Christians do not die in bed. God does not allow them to live out their full amount of years. God jerks them up short and takes them home to be with Him. He takes them home with a dishonorable discharge. That is a miserable way to go home to meet God. God saves their soul so as by fire. He saves some people by the skin of their teeth.
1 Co 3: 15 “If anyone’s work is burned, he will suffer loss; but he himself will be saved, yet so as through fire.”