It's not that people cannot work for it, it's just that people will always want to do more, will always want to prove something, will always want to have one more star, their name in lights, on the silver screen...men will always need approval for their efforts.
Men can attempt to do right but at one point the line between doing right and motive for doing right will be lost. Sooner than later, you won't be giving because it is the right thing to do but rather because you want to receive applause for giving the bigger amount. Didn't the pharisees blow their own trumpets before they gave alms?
Righteousness can not be attained through our works, because somewhere along the way, superlatives will come into play.
Adam levelled the ground, out of him reduces us all to failure. Which is why we need grace. Grace demands no superlatives. Grace will take the best or the worst, the cleanest or filthiest. The shortest or tallest. The wisest or stupidest.
No need to pull rope trying to prove I am better than you. His blood makes us all acceptable.
Forget your goodness, your wealth, your wisdom, there are earthly merits. When it comes to God, the only merit is grace and faith in the Lord and Saviour Jesus Christ.