Where Does Shiva Come From?
We only see from this verse that there is an obligation to mourn, not how long one must do so. So where does the practice to “sit shiva” come from?
“Sitting shiva” – that is, mourning for seven days – is not a Biblically-mandated practice per se but it does have a precedent in the Torah: Joseph mourned his father Jacob for seven days (see Genesis 50:10 – “…he mourned his father seven days” – and Talmud Yerushalmi Moed Katan 3:5). One might fulfill the Biblical obligation to mourn by doing so for a single day but according to the Talmud Yerushalmi (Kesubos 1:1), it was Moshe who instituted that we should mourn for seven days as Joseph did. (Moshe also institutionalized the week of wedding celebration – “sheva brachos” – which likewise has precedent, in Genesis 29:27.)
Another Biblical allusion to shiva is found in the Book of Amos (8:10). There, the prophet warns the people that if they do not change their ways, God will “turn your festivals into mourning.” The Talmud in Moed Katan (20a) points out that the festivals of Pesach and Succos are each seven days. Similarly, the mourning period is seven days. (The Talmud asks: what about the festival of Shavuos, which is just one day? It answers that sometimes there is a one-day mourning period. Specifically, this is the case when one learns of a close relative’s passing long after the fact.)
The deceased’s relatives are not the only ones to observe shiva. According to the Talmud in tractate Shabbos (152a), the deceased’s own soul also mourns for the loss of its body. This is derived by juxtaposing the verses “his soul mourns for him” (Job 14:22) and “he mourned his father seven days” (Genesis 50:10).
The mourning period does not begin until after the burial. After shiva concludes, a lesser degree of mourning is observed until the end of thirty days; this period is called “shloshim.” For a parent, a still less-intense form of mourning is observed until the conclusion of 12 months, though Kaddish is only recited for 11 months.