Romans 4:1-3 What will we say then that Avraham our father, as pertaining to the flesh, has found? For if Avraham were justified by works, he has something to boast about; but not before G-d. For what said the scripture? Avraham believed G-d, and it was counted unto him for righteousness.
By works - Legalistic observances
Paul says G-d's righteousness is imputed to us.
Avraham believed G-d and was accredited with G-d's righteousness.
David and Avraham are our examples.
Romans 4:4-8 Now to him that works is the reward not reckoned of grace (mercy), but of debt. But to him that works not, but believes on him that justifies the ungodly, his faith/trust is counted for righteousness. Even as David also describes the blessedness of the man, to whom G-d imputes righteousness without works, Saying, Blessed are they whose iniquities are forgiven, and whose sins are covered. Blessed is the man to whom the L-rd will not impute sin.
David committed murder and adultery yet righteousness was imputed to him. Is this just?
Answer: Yes, because we all fall short when it comes to G-d's standard of perfection. (Jew and Gentile)
Romans 4:9-10 Is this blessing then upon the circumcised, or upon the uncircumcised also? For we say, "Faith was reckoned to Abraham as righteousness." How then was it reckoned? While he was circumcised, or uncircumcised? Not while circumcised, but while uncircumcised;
Paul claims "circumcision" is of no effect in regards to salvation. The Gentiles whom are not circumcised are blessed by G-d also.
This reminds me of the thief on the cross. He was guilty, yet all Yeshua required was that he believe in Him and that Yeshua's blood covered his way to redemption. The thief did not have to do anything else to enter into paradise. Salvation only requires "faith" alone. He did not have to be immersed (baptized), circumcised, or do anything else.