Lightbulb

Rav Yitchak David Grossman:

If you paint a lightbulb black you would not be changing the purity of that light, even if you might be covering its external body.

So too with a neshama- no matter how irreligious or how "black" a neshama seems to be, this is only a covering. Underneath it all is still a yid with the same "energy" we were all created with, a direct energy from The Source.