sin
"Sin" in Romans 6, 7 is the nature in distinction from "sins," which are manifestations of that nature.
Compare (1 John 1:8) with (1 John 1:10), where this distinction also appears.
grace
Grace (in salvation). (Romans 5:2); (Romans 5:15-21); (Romans 11:5-6); (Romans 3:24).
( See Scofield) - (John 1:17).