"If anyone sees his brother committing a sin not leading to death, he shall ask and God will for him give life to those who commit sin not leading to death. There is a sin leading to death; I do not say that he should make request for this. 17 All unrighteousness is sin, and there is a sin not leading to death," (1 John 5:16-17).
The meaning of verses 16 and 17 is debated among Christians. There is no absolute consensus on what this means. But, generally speaking, we conclude that there sins that people can commit which God takes seriously enough so as to end their lives. An example of this is of Ananias and Sapphira--in Acts 5:1-10--who lied to the Holy Spirit. God judged them for this and both were killed.
"But a certain man named Ananias, with his wife Sapphira, sold a piece of property, 2 and kept back some of the price for himself, with his wife’s full knowledge, and bringing a portion of it, he laid it at the apostles’ feet. 3 But Peter said, “Ananias, why has Satan filled your heart to lie to the Holy Spirit . . . 5 And as he heard these words, Ananias fell down and breathed his last; and great fear came upon all who heard of it . . .7 Now there elapsed an interval of about three hours, and his wife came in, not knowing what had happened. 8 And Peter responded to her, “Tell me whether you sold the land for such and such a price?” And she said, “Yes, that was the price.” 9 Then Peter said to her, “Why is it that you have agreed together to put the Spirit of the Lord to the test? Behold, the feet of those who have buried your husband are at the door, and they shall carry you out as well.” 10 And she fell immediately at his feet, and breathed her last," (Acts 5:1-3, 5, 7-10).
Another sin that is associated with death is found in 1 Corinthians 5:1-5 where it is reported that a man was having sexual relations with his father's wife.
"It is actually reported that there is immorality among you, and immorality of such a kind as does not exist even among the Gentiles, that someone has his father’s wife. 2 And you have become arrogant, and have not mourned instead, in order that the one who had done this deed might be removed from your midst. 3 For I, on my part, though absent in body but present in spirit, have already judged him who has so committed this, as though I were present. 4 In the name of our Lord Jesus, when you are assembled, and I with you in spirit, with the power of our Lord Jesus, 5 I have decided to deliver such a one to Satan for the destruction of his flesh, that his spirit may be saved in the day of the Lord Jesus," (1 Cor. 5:1-5).
Blasphemy of the Holy Spirit is another sin certainly worthy of death. God gives those who commit the sin over to the depravity of their hearts and minds, and they are beyond redemption. Some believe that blasphemy of the Holy Spirit is a sin that leads to death. At the very least, it ensures damnation.