Arizal On Ki Teitzei and Elul

The Arizal explains this week's parsha (Sefer Halikutim) in a very inspiring manner: he stars off with the verse regarding Cain: "evil crouches at the doorpost," and explains that this refers to every Jew. Every Jew starts off with the Yetzer Hara and only receives the Yetzer Tov when he is thirteen years and one day old. But one's limbs are already accustomed to working with the Yetzer Hara from day one. When a person wishes to do teshuvah, this represents going out to war against his enemies as the first verse in our parsha discusses. And Hashem will give them into your hands," This refers to the Yetzer Hara. "And you will take captives," that is you will regain mastery over your limbs. "And you will see an eishes yefas to'ar," this refers to the neshama. "And you will bring her into your house and she will cut her hair" this refers to obliterating all emunos ra'os, bad faiths in your head." "And shorn her nails." means that you will cut away all connection to unnecessary materialism. "And she will remove the garment which she had on when she was captured," that is the evil garments that were on his neshama as a result of all of his sins as the verse states, "Remove your soiled garments." After this she will cry for her Father," this represents Hashem. "and her mother," this represents all of Israel [which was distanced as a result of his sins since all Jews are connected]." "For a month's time," this is the month of Elul, since in this context, the month means days and not years and Elul is a time that is fitting to do teshuvah.
In a different place on the parsha: Rav Chaim Vital explains that a Bar Mitzvah parallels our exile from Egypt. The seven days of the holiday represents the seven years from Bar Mitzva until twenty. One must be careful to avoid chametz and seor especially during these years. If he does so, he will merit to avoid sin later with much greater ease. The fourty nine days of the Omer represent the next fifty years of life, when one must continue to hold a strong vigil and strive to prepare to connect to Hashem. If he merits this then at the fiftieth day/year he attains the level of Matan Torah regarding which it says that Hashem spoke "face to face."