"...First, it is true that St. Paul does not say works of law in Romans 4:5. But the context makes it very clear that St. Paul was referring to circumcision in particular and the same “works of law” he was referring to in Romans 3:28. Romans 3:28 down to Romans 4:5 represents one continuous thought in answering the Judaizers and their insistence upon circumcision and keeping the Old Covenant in order to be saved."
In verse two, Paul says "justified by works." In verse four, he refers to "the one who works." In verse six, Paul says that one is justified by faith "apart from works." In this context, he even uses Abraham who was not under the Levitical system as his first example. There is no reason to believe that "works of the Law" applies only to works of the ceremonial law. Also, the New English Translation has this footnote on Romans 3:20:
Paul says that the Law is holy, righteous, and good (Romans 7:12; 16). In other words, it reflects the character of God. Thus, there exists no new law by which we can be justified. Romans 7:6-7 is a problem for Tim's position because it shows us that Paul had much more than circumcision in mind when mentioning works of the Law. He even distinguishes between circumcision and following commandments (1 Corinthians 7:19). Consequently, Paul excludes the moral aspects of the Law as grounds for justification before God. He goes as far as to say that love fulfills the Law (Galatians 5:14). There is not a single good work that does not fit into that category. The Apostle Paul does not say that we "can only perform salvific acts in Christ." It is always by faith (Galatians 3:1-3).
"Just so no one would get the wrong idea of what St. Paul was saying, it seems, he put it plain and simple in Galatians 5:19-21 and 6:7-9. There is no way we can get “justification by faith alone” that excludes works as necessary for justification in any and every sense if we read these texts carefully. St. Paul makes clear that if Christians allow themselves to be dominated by their “flesh,” or lower nature, they will not make it to heaven."
In Galatians 5:19-21, the Apostle Paul contrasts works of the flesh with works of the Spirit. In Galatians 6:7-9, he states that the wicked will face eternal judgement. These passages, however, are not related to the instance of justification. They are different contexts. Galatians 2:16, 3:11, and 3:22 are clear that justification is not obtained by works.
In Romans 3:27, Paul raises a rhetorical question: "By what kind of law? Of works?" If there was some new law which we could obey to get saved from eternal condemnation, then this would have been the ideal place for him to mention it. But that does not happen. What Paul is arguing against is the law of works. He is excluding works in general.
The Roman Catholic Church shares a glaring parallel with the Judaizers, who claimed that believers needed to revert to observing the Law in addition to faith in Christ for salvation. The Roman Catholic Church denies the sufficiency of faith as the instrument of justification by adding sacraments. Both groups mix Law with grace. Such was categorically condemned by the Apostle Paul as a false gospel (Galatians 1:6-12).