This is one of the more opaque songs on the album. The key to it may lie in the circumstances surrounding the making of St. Anger
The band was experiencing a lot of friction. Bassist Jason Newsted had left on rough terms after asking for some time off to pursue a side project called Echobrain. Frontman James Hetfield's drinking had worsened to the point where he had to leave in the middle of recording to check into rehab. The band was still dealing with fallout from their battle with Napster, where an unauthorized demo of their song "I Disappear
" showed up. On top of that, the band was frustrated with their label's continued pressure to do promotional work, as documented in the song "Sweet Amber
Basically, things were a mess. "Purify" seems to be Hetfield saying he wants to be cleaned of the past and of himself while acknowledging his own tendency to pessimism ("I can find the dirt on anything").