Holy scripture makes a distinction between mortal and non mortal sins. In the KJV these two categories of sin are called a sin unto death and a sin not unto death. The passage in which these words are used is this:
1 John 5:16-17 (16) If any man see his brother sinning a sin not unto death, he shall ask, and God will give him life for them that sin not unto death. There is a sin unto death: not concerning this do I say that he should make request. (17) All unrighteousness is sin: and there is a sin not unto death.
On the matter of a sin not unto death
WORD PICTURES IN THE NEW TESTAMENT by Archibald Thomas Robertson observes:
Not unto death (mē pros thanaton). Repeated again with hamartanousin and in contrast with hamartia pros thanaton (sin unto death). Most sins are not mortal sins, but clearly John conceives of a sin that is deadly enough to be called “unto death.” This distinction is common in the rabbinic writings and in Num 18:22 the LXX has labein hamartian thanatēphoron “to incur a death-bearing sin” as many crimes then and now bear the death penalty. There is a distinction in Heb 10:26 between sinning wilfully after full knowledge and sins of ignorance (Heb 5:2). Jesus spoke of the unpardonable sin (Mark 3:29; Matt 12:32; Luke 12:10), which was attributing to the devil the manifest work of the Holy Spirit. It is possible that John has this idea in mind when he applies it to those who reject Jesus Christ as God’s Son and set themselves up as antichrists.
Numbers 18:22 The Israelites will no longer approach the Tent of Meeting, on pain of committing a deadly sin.
Of course there were a number of sins that carried the death penalty under the Laws of Moses these would not doubt be considered deadly sins under that covenant. Under the new covenant the sins that appear to carry a very serious penalty are included in various lists; among those listed are these:
Revelation 21:6-8 (6) And he said unto me, It is done. I am Alpha and Omega, the beginning and the end. I will give unto him that is athirst of the fountain of the water of life freely. (7) He that overcometh shall inherit all things; and I will be his God, and he shall be my son. (8) But the
- fearful, and
- unbelieving, and
- the abominable, and
- murderers, and
- whoremongers, and
- sorcerers, and
- idolaters, and
- all liars,
shall have their part in the lake which burneth with fire and brimstone: which is the second death.
The scriptures list a number of sins that are sufficient to separate a person from God.