If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it [1 John 5:16].

“Death” refers here to physical death. It has no reference at all to spiritual death because the child of God has eternal life. John is saying that believers can commit a sin for which their heavenly Father will call them home; that is, He will remove them from this life physically, perhaps because they are disgracing Him.

Let us look at some people in Scripture who have committed a sin unto death. Moses and Aaron committed a sin unto death. You will recall that Moses got angry when the children of Israel kept begging for water and, instead of speaking to the rock as God commanded him, he smote the rock twice. He shouldn’t even have touched that rock. It had already been smitten once before, and he should have rested upon that. The rock was to be an example and a type of Christ. Paul wrote, “And [the children of Israel] did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ” (1 Cor. 10:4). Christ died only once, and Moses spoiled the type by striking the rock twice. “And the LORD spake unto Moses and Aaron, Because ye believed me not, to sanctify me in the eyes of the children of Israel, therefore ye shall not bring this congregation into the land which I have given them” (Num. 20:12). There was for this man Moses a restoration in that he could continue leading. However, he began to plead with God to forgive him and to permit him to enter the land, but the Lord told him in effect, “Although I have restored you to your place of leadership, you are not going to enter the land.” When Moses kept after the Lord, the Lord said to him, “… speak no more unto me of this matter” (Deut. 3:26). Moses and Aaron both had sinned a sin unto death—physical death.
In the New Testament we have another example of this in Ananias and Sapphira. They were a part of the early church, and they were guilty of a lie (see Acts 5:1–11). They had been willing to give a false impression to the early church; they were willing to live a lie. Because of that, God removed them from this earthly scene.

There is another incident of this mentioned in 1 Corinthians. Some of the people there had actually been getting drunk at the Lord’s Supper, and they were missing the meaning of it altogether. Paul wrote to them, “For this cause many are weak and sickly among you, and many sleep” (1 Cor. 11:30, italics mine)—that is, they were dead. Paul is saying that they had committed a sin unto death.

Someone might ask at this point, “What is a sin unto death?” First, let me be clear that John was not speaking of an unpardonable sin. We are talking about a sin unto physical death, not spiritual death. These people were God’s children. He would never have taken them home if they had not been His children. The Lord doesn’t whip the Devil’s children—He whips only His own. When His children sin unto death, He will take them home.

What is this sin? What is it specifically? Well, for Moses and Aaron it was one thing—they lost their tempers, and they destroyed a type of the Lord Jesus. Ananias and Sapphira were living like hypocrites. And in the city of Corinth, there were believers who were getting drunk and were disorderly at the Lord’s Table. So a sin unto death is no one thing specifically. I have a notion that for you it would be different from what it would be for me, but I am of the opinion that every believer is capable of committing the sin unto death—whatever it is for him. You can go on in sin until God will remove you from the scene. This does not mean that every Christian who dies has committed the sin unto death, but it is possible to do that.

Absalom also committed a sin unto death. I believe that Absalom was really a child of God, but he led a rebellion against his father, King David. I have observed something over a period of years. I have watched how God has dealt with troublemakers in the church. I’ve not only seen Him remove them by death, but I’ve also seen Him set them aside so that they were of no more use in the service of God at all. It is possible to commit the sin unto death. Let me repeat that it is physical death not spiritual death.

Let me illustrate this. There is a mother who has a boy, Willie—her little angel child, of course. Next door, though, there lives a little brat about the age of her little angel, and they play together out in the backyard. One day as she is working in the kitchen, she hears that little brat yelling at the top of his voice. She rushes to the door, looks out, and there is her precious little angel on top of the little brat next door, just beating the stuffing out of him! She says, “Willie, you are going to have to come into the house if you are not nice to the little boy next door.” He says, “Yes, Mama. I’ll be better.” She says, “Well, if you are not, I’m going to have to bring you in the house.” So she goes back in, and about thirty minutes go by, but again she hears that familiar cry of the little brat next door. She goes to the door, and the same sight greets her. Her precious little angel is on top of the brat next door, just beating the stuffing out of him. She says, “Willie, come into the house.” He says, “I don’t want to come into the house.” She says, “I said that if you did that again, you would have to come into the house!” So what does she do? She goes out and gets him by the hand, and she takes her precious little angel, yelling at the top of his voice, into the house. He had to come in. He may not be her precious little angel anymore, but he still is her son—that fact never was disturbed, but he can no longer play outside. I think that if a child of God goes on disgracing the Lord down here, the Lord will either set him aside or take him home by death. God doesn’t mind doing that. I think He does it in many instances.

McGee, J. V. (1991). Thru the Bible commentary: The Epistles (1 John) (electronic ed., Vol. 56, pp. 158–161). Nashville: Thomas Nelson.