Are the Good Works of Christians Filthy Rags?

The following quote is from The Practice of Piety (1612) by Lewis Bayly. In this part of the book, he notes hinderances to the practice of piety which arise from misunderstanding passages in Bible. In this paragraph, he addresses a common misunderstanding of Isaiah 64:6 and explains a doctrine which would a few decades later be included in our Presbyterian confession of faith (WCF 16.6, see here). This doctrine is that when we are forgiven and accepted through faith in Christ, on that basis our imperfect but sincere obedience which is produced in us by God’s grace is pleasing to God. God delights in the good works of His children and graciously accepts their services through the intercession of Jesus Christ (1 Peter 2:5). Here is what Bayly says:

"Isa. 64:6, 'All our righteousnesses are as a filthy rags.' Hence the carnal Christian gathers, that, seeing the best works of the best saints are no better, then his are good enough; and therefore he needs not much grieve that his devotions are so imperfect. But Isaiah means not in this place the righteous works of the regenerate, as fervent prayers in the name of God; charitable alms from the bowels of mercy; suffering in the gospel's defense, the spoil of goods, and spilling of blood, and such works which Paul calls the fruit of the Spirit (Gal. 5:22;) but the prophet, making an humble confession in the name of the Jewish church, when she had fallen from God to idolatry, acknowledges, that whilst they were by their filthy sins separated from God, as lepers are from men by their infecting sores and polluted clothes, their chief righteousness could not be but abominable in his sight. And though our best works, compared with Christ's righteousness, are not better than unclean rags; yet, in God's acceptation for Christ's sake, they are called white raiment (Rev. 3:18), yea, pure fine linen and shining (Rev. 19:8)..."