keeping the Law & knowing what sin really is.

Thomas Schreiner is spot on:

"...If the law could be kept perfectly, then people would deserve salvation and therefore could boast. However, since all people sin and fall short of the glory of GOd, it is a great delusion for sinners to think that they can earn merit before God by their works. Paul condemns boasting in works because no one can possibly do all the works God requires. Human beings, though, are naturally given to idolatry (Rom.1:18-25), and thus they deveive themselves into believing that their obedience to the law somehow suffices to impress God and warrant salvation. Such folly stems from the failure to see how gloriously perfect God is, and how infinitely repugnant sin is to God" (The Law & Its Fulfillment, p.114).

Magnificently stated!