R' Chaim Vital writes in the name of the Arizal: Every person has a set day in the week and in the month that is a day that is good for him for all his matters because his mazel depends on the day according to the root of his soul. And on that day, he shouldn't fear that anything bad will happen to him and he will not die on that day.
Shaar Hagilgulim, Hakdama 38.
R' Chaim Vital (Shaar Hamitzvos, Parshas Eikev) writes that his Rebbe, the Arizal, wouldn't wear excessively nice clothing for himself and also ate very little. However regarding his wife’s clothing, he was very careful to honor her and to dress her and would fulfill her wishes, even when he couldn’t afford it.
In this way we can understand ושוב יום אחד לפני מיתתך, repent one day before your death: There is no fear that on that day he will die, and therefore he should do teshuva on that day, because on the other days there is that fear that he will die. R' Chaim Vital continues “The Arizal told me that my day in the week according to my root soul is Monday and my day in the month is the 13th of the month.”
Avos 2:15.
