I think the answer might be:
Althought I can't fit it to all the lines.
“It's cold and hard and doesn't bend,”
in just ice: ice has those properties
“Can bring a life to a speedy end:”
injustice can get you hanged (if you are (extremly) unjust), get you killed (if you are the victim of an unjust person). Also I like @micsthepick and @Ctx use of ice.
“It's neither cruel nor kind nor nice.”
I have no idea. Maybe in justice (as justice is neither cruel nor kind nor nice).
“Your faults and you it judges well:“
in justice: justice provides the laws and rules to judge peoples faults and give them the right punishments.
“Too much and you can go to hell;”
This one fits 100%. Too much injustice from you and you are definetly going to hell.
"If not, on it you'll cross the abyss."
No freaking idea.