What does Romans 3:4 mean?
In the previous verse, Paul imagined someone asking a pointed question: If the Jewish people broke the law of God, does that mean He will no longer be faithful to them?Paul answers with one of his favorite emphatic phrases. In modern English, this might be stated, loudly, as "no way!" In Greek, it reads "mē genoito," literally meaning "let it not be" or "may it never be so." English translations use the phrases such as "God forbid," "Not at all," and "By no means!" This exclamation is repeated many times in Romans.
Paul insists that God's faithfulness does not depend on human faithfulness. The sentence, "God will be true even if every man is a liar" may come from Psalm 116:11. Then Paul quotes directly from Psalm 51:4 to describe this aspect of God's character: "That you may be justified in your words, and prevail when you are judged."
In other words, God always keeps His word and remains faithful to His people no matter what they do. That's why His words and judgments are justified. He never ever breaks His side of any covenant agreement.