"But we are all like an unclean thing, and all of our righteousnesses are like filthy rags" (Isa. 64:6).Reference Isaiah the prophet summed up the wretched state into which the covenant people of God had sunk. Though they had the boon of receiving the Law from Mount Sinai, though they had come out of Egypt through the Red Sea, they had turned from their Lawgiver. The children of Zion were worshipping false gods (42:17). They were reveling in the dregs of idolatry. So much so, the prophet calls Jerusalem a harlot (1:21) and likens it to Sodom (3:9).
And yet, the people had an illusion of righteousness. Some of them professed to be "holier than thou," even while burning incense on strange altars (65:3-5). But God did not esteem their righteousness to be anything but pollution. He even hated the Sabbaths and feasts that He had Himself ordained (1:13,14). The house of Jacob's apostasy had rendered its best acts of religion unclean. Like the wind, sins were sweeping people away (64:6b).
How appropriate that the prophet would break into such hyperbole as to call this supposed goodness "filthy rags." What better way to call the nation to repentance? In the context of proud Judah's barrenness, the rebuke comes with the force of a thunderbolt.
This is most certainly the way the text should be read. We have all heard that "a text without a context is a pretext." This applies here. The "filthy rags" must be understood historically and with application to the audience: apostate Jerusalem.
This, however, is not the way many Evangelical Protestants applies the famous passage. In fact, in all of the times I have ever heard it quoted - in sermons, study guides, books, Sunday School lessons - I have never once heard anyone interpret the verse in context. References to Isaiah 64:6 are invariably made to mankind in general. The verse becomes a proof-text for the total depravity of man - even of the saints. Many will say that the deeds of even the most profound disciples are nothing but "filthy rags" in the sight of God. And so, the text is made universal and theological, rather than specific and historical.
The Isaiah text has long functioned as support for the "orthodox" creeds and confessions. Calvinism uses it to establish the idea that everything the natural man does is wicked - even good deeds. This helps to set up the dogma of "total inability," the engine which drives the entire Calvinist soteriology.