The Great Commentary of Cornelius à Lapide
1 John 1:17
A11 iniquity is sin, and there is a sin unto death : the Greek and Syriac add the negative proposition, and there is a sin not unto death. He opposes the two kinds of sin. Every iniquity is sin, but not every iniquity unto death, because it is a peculiar kind of sin which, as is said, is sin unto death.
For iniquity the Greek has α̉δικία, injustice, which is properly opposed to justice. But as in Scripture, so also in Aristotle and the ethical writers, justice is taken generally for any virtue, and injustice or iniquity for any sin.