He says, that believers have no righteousness of their own. Now, it cannot be denied, that if there were any righteousness of works, it might with propriety be said to be ours. Hence he leaves no room whatever for the righteousness of works. Why he calls it the righteousness of the law, he shows in Romans 10:5; because this is the sentence of the law, He that does these things shall live in them. The law, therefore, pronounces the man to be righteous through works. Nor is there any ground for the cavil of Papists, that all this must be restricted to ceremonies. For in the first place, it is a contemptible frivolity to affirm that Paul was righteous only through ceremonies; and secondly, he in this way draws a contrast between those two kinds of righteousness—the one being of man, the other, from God. He intimates, accordingly, that the one is the reward of works, while the other is a free gift from God. He thus, in a general way, places man’s merit in opposition to Christ’s grace; for while the law brings works, faith presents man before God as naked, that he may be clothed with the righteousness of Christ. When, therefore, he declares that the righteousness of faith is from God, it is not simply because faith is the gift of God, but because God justifies us by his goodness, or because we receive by faith the righteousness which he has conferred upon us. (Calvin on Phil 3:9)
More good stuff.
Paul makes no bones about it. “If you want to play that works game, then you had better keep all those laws and keep them perfectly. And then you no longer require Christ, and sever yourself from Him.” (paraphrased)
Like Jesus told the rich young ruler after he thought he had kept the commandments from his youth up, “This one thing you lack…” That’s all it takes, one jot or tittle undone and your doomed. There is no one who does good, no not one.
For whoever keeps the whole law but fails in one point has become accountable for all of it. James 2:10