All unrighteousness is sin
All unrighteousness against God or man is a sin against the law
of God, and the wrath of God is revealed against it, and it is
deserving of death; yet all unrighteousness is not unto death, as
the sins of David, which were unrighteousness both to God and
man, and yet they were put away, and he died not; Peter sinned
very foully, and did great injustice to his dear Lord, and yet
his sin was not unto death; he had repentance unto life given
him, and a fresh application of pardoning grace:
and there is a sin not unto death;
this is added for the relief of weak believers, who hearing of a
sin unto death, not to be prayed for, might fear that theirs were
of that kind, whereas none of them are; for though they are
guilty of many unrighteousnesses, yet God is merciful to them and
forgives, ( Hebrews 8:12
) , and so they are not unto death.