It has become quite common to abuse the scriptural phrase “beauty for ashes” to mean that we can offer God nothing more than ashes because we are naturally sinful so we’re just going to misbehave anyway and that is OK because he will bless us with beauty even though we only offer ashes. This abuse of the scripture takes two forms, one in which we offer ashes by really offering no good behavior and we abuse the scripture to mean that he will bless us anyway. In the other abuse of this scripture we offer ashes by being sad about our sins, but not sad to the point that we actually change anything, because the idea is that we really can’t do any better than misbehaving anyway.
The word “ashes” here is a reference to “sackcloth and ashes”. It is telling wicked Israel that if they will repent and forsake their sins the Lord will bless them with beautiful cleanliness through forgiveness.
There is a world of a difference between the message that if we will repent and forsake our sins the Lord will bless us with beautiful purity, and the message that we can excuse our sins by invoking the “natural man” as an inescapable standard of behavior, and the Lord recognizes that we can’t do any better and will bless us anyway.