Romans 4:4

New International Version

Now to the one who works, wages are not credited as a gift but as an obligation.

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“Who has ever given to God, that God should repay them?”

And if by grace, then it cannot be based on works; if it were, grace would no longer be grace.

and all are justified freely by his grace through the redemption that came by Christ Jesus.

Why not? Because they pursued it not by faith but as if it were by works. They stumbled over the stumbling stone.