P. 12 in the text of the Tanya, P. 262 in the commentary. (7th perek). After death, the body is purified from the impurities brought upon it through using the permitted with the wrong intentions, as well as indulging in the assur (forbidden). The tzadikim do not have the same longing and thirst for Elokus (G-dliness) as someone who is very far from Hashem. Proper teshuvah can return the sparks of kedusha that have fallen into the dark places. The nefesh habehamis (animal soul) of a Jew only wants to satisfy physical desires. When we think, speak, and do with the proper kavanos (intentions), we are serving Hashem in the proper way. Poverty can make a person as obsessed with the physical world as wealth.