Question: I have heard that there is a Jewish concept known as the "fifty levels of defilement". Would you recommend a source that would name and explain these "levels of defilement"?
Answer: The tumah (ritual impurity or defilement) caused by a corpse and other impurities is divided in halakhah (Jewish law) into only six levels. My colleague, Ina Rubin Cohen, suggested that you are referring to the "fiftieth gate of tumah" that the Jews would have descended to had they remained in Egypt a moment longer then they had (see, for example, the Bible commentary Or ha-Hayim, by Rabbi Hayim ibn Atar, on Exodus 3:7 s.v. va-yomer Hashem ra’oh raiti). This concept of tumah is not a halakhic one related to ritual impurity, but rather a kabbalistic one that uses the term "tumah" to indicate sin and estrangement from God. See: http://en.wikipedia.org/wiki/Sefirot#Latent_interinclusion_of_the_Sephirot, where it discusses the concept of 49 gates of holiness that correspond with the counting of the Omer. The holiday of Shavuot represents the fiftieth gate of holiness that encompasses the other 49. In kabbalistic thought what exists on the side of holiness is mirrored on the side of impurity. Hence, the Jews had descended to the 49th gate of impurity in Egypt. Had they remained any longer they would have fallen to the fiftieth and been lost. Through the redemption from Egypt and improving themselves during the 49 days between leaving Egypt and receiving the Torah on Mt. Sinai they merited to leave the 49 gates of impurity and ascend through the 49 gates of holiness. On the fiftieth day they received the Torah. During the counting of the Omer we reenact this process every year. A good book for introducing kabbalistic concepts is Innerspace by Rabbi Aryeh Kaplan [Jerusalem : Moznaim, 1990].