“And I will sprinkle clean water upon you, and ye shall be clean; from all your uncleannesses, and from all your idols, will I cleanse you.”
– Ezekiel 36:25, JPS 1917 Tanach
The B’nei Yisrael (Children of Israel) had sunk to the 49th level of impurity in Egypt. Had we descended to the 50th level of impurity, according to chazal, we would have been indistinguishable from the Egyptians. From this perspective, we were not brought out of Egypt, based upon our own merit. This is akin to what is mentioned later in Torah, “Not for thy righteousness, or for the uprightness of thy heart” (Deuteronomy 9:5).
Thus, we were taken out of Egypt by way of what is called itaruta dil’eyla, an “awakening from above,” wherein H’Shem brings about an effect from Shomayim. From out of the influence of an idolatrous society, B’nei Yisrael was freed from slavery, in order to serve H’Shem.
The 49 day counting of the Omer, between Pesach and Shavuos is a gradual ascent to the 49th level purity. A time to effect a gradual transition to a positive set of character traits, through an itaruta dil’tata, an awakening from below, i.e., from our own efforts. As B’nei Yisrael spent forty nine days on a journey from Egypt towards Mount Sinai, where the Torah was given, so opportunity given the opportunity to prepare ourselves to receive the Torah anew on Shavuot.