But doesn’t God do us an injustice by requiring in His law what we are unable to do?
No, God created human beings with the ability to keep the law. They, however, provoked by the devil, in willful disobedience, robbed themselves and all their descendants of these gifts.
Scripture references
Does God permit such disobedience and rebellion to go unpunished?
Certainly not. God is terribly angry with the sin we are born with as well as the sins we personally commit.
As a just judge, God will punish them both now and in eternity, having declared: “Cursed is everyone who does not observe and obey all the things written in the book of the law.”
But isn’t God also merciful?
God is certainly merciful, but also just. God’s justice demands that sin, committed against His supreme majesty, be punished with the supreme penalty— eternal punishment of body and soul.