is an archaic variation of . It's still common in fiction, especially fantasy. See these questions:
* Grammar of (verb)(noun) such as in
* [In "[V stem] + + [noun]" what does mean?](
* What does the kana do in this phrase?
As for itself, I personally feel its meaning is closer to "to wander about" rather than "to be lost" here, because it's clearly moving (). See .
Note that is a relative clause that modifies , so it's the ("impurity/corruption") itself that is wandering about. It's "steps of wandering impurity" rather than "I take an impure walk".