Why does the Torah insert the word "Kol ha'Mishkav ... "
Refer to 15:4:1:1*.
Sifra: To teach us that whatever is designated for Mishkav is subject to YTu'as Mishkav
Perhaps the Sifra learns this from the 'Hey' of "ha'Mishkav".
Why does the Torah insert the (otherwise superfluous) word "ha'Zav"?
Sifra: To preclude a Ba'al Keri, an Even ha'Menuga'as, a Tamei Meis and a Meis from the Din of Mishkav and Moshav. 1
See Torah Temimah, note 19.
Why does the Torah write "Asher Yishkav alav " and "Asher Yeishev alav ... " (in the future)?
Rashi and Targum Yonasan: To teach us that it the article is only subject to Tum'as Mishkav if it is designated exclusively for lying on or for sitting on, 1 but not if one needs to ask the person who is lying or sitting on it to get up and allow the owner to use it for whatever it is designated for ('Amod ve'Na'aseh Melachteinu!')
The Sifra learns this from the word "Kol ha'Mishkav asher Yishkav alav", which is otherwise superfluous.
What will be the Din if the Zav does not actually touch the article on which he is lying?
Rashbam: A Zav, a Zavah or a Nidah who is lying or sitting on a stone 1 which is placed on top of a bed or sheet, which he is not touching (E'ven Mesamei), adopt Tum'as Mishkav or Tum'as Moshav, to be Metamei a person and the clothes he is wearing.
And the same will apply even to the bottom sheet, if he is lying on top of ten sheets.
Why does the Torah write the word "Yitma" twice?
Sifra: To include in the Din of Mishkav and Moshav, someone who lies on a seat or who sits on a bed, and someone who stands hangs or leans on on anything that is made to bear one's weight.
In what ways is a Zav Metamei a Mishkav or Moshav?
Moshav Zekenim (in Pasuk 33, citing the Rambam): It is through sitting, lying, hanging, leaning or being carried on it.
