Christ fulfilled ALL the righteous requirements of the Law.
ALL of it.
Through faith, that righteousness is imputed to us by God Himself.
We are then clothed in the righteousness of Christ. When God looks at us, He sees us as righteous as Christ is because He sees CHRIST’S righteousness.
Adding our own works to that to earn salvation is an exercise in futility.
How can our allegedly good works, twisted and corrupted by sin as they are, be added to the perfect, holy righteousness of Christ we already possess as God’s children through faith to gain salvation? How can perfection be improved upon by imperfection?
The very idea is ludicrous.