Isaiah 64:6

Finally, just as our goodness with regard to the goodness above becomes like evil, so our righteousness compared with divine righteousness is like menstrual rags. This is considered to be so by Isaiah the prophet: "All our righteousnesses are like menstrual rags." For although there is much of good works of the saints, nevertheless they are preoccupied with earthly endeavor and this holds them back and stops them from the contemplation of that higher good.

Some translators try to alter the meaning of this passage.… For it is not, they say, that the divine anger was the cause of their misdeeds, but that because they misbehaved, God was angry. For they are afraid lest God's anger be thought of as the effector of sins. I think it ought to be said that there is no condemning the divine anger, if those receiving it were insufficiently motivated to flee the attack of sin. As long as the Savior is pleased in us, let us flee sin and forcefully leave the filth of vices and with increase be crowned in spiritual success.… For God is the Lord of powers.… Just as the kind clemency from above shows us how to be strong and brave for the resistance of evil, by the same reason when we fall under divine wrath, it is necessary that we bow in servile fashion.

And whatever righteousness we appear to have is compared to the rag of a sitting or menstruating woman. For which Theodotion put the Hebrew word Eddim, which Symmachus interpreted as κυουσῶν, that is, of those giving birth; Aquila as μαρτυριῶν, that is, of testimonies: when blood is approved in the first marital union of a virgin. And we have fallen away, he says, like leaves from trees, which are scattered by the blasts of the winds because of our iniquities. In this, it should be considered that the righteousness which is in the Law is called impurity in comparison to the purity of the Gospel. For what was once glorified is not glorified anymore because of the surpassing glory. Therefore, the apostle Paul, who had fulfilled everything according to the righteousness which is in the Law, says that he has considered all things as loss in order to gain Christ (Philippians III), and because of the surpassing knowledge of our Lord Jesus Christ, for whom he considers everything as worthless, so that he may gain Christ and be found in Him, not having his own righteousness which is from the Law, but the righteousness which comes from God through faith in Christ. For he is just who dies in his own righteousness (Eccles. 7), if after the truth of the Gospel he wishes to exercise legal shadows, and not to pursue what is justly just.