Who are "ha'Overim ba'Aretz"?
Rashi: Passersby who see human bones.
What do we learn from "Etzem"?
Malbim: After the seven months, there will not be bones with flesh, only bones.
What is "Tziyun"?
Mo'ed Katan (5a): This is an Asmachta for the tradition from Sinai that one must mark off graves 1 . Rashi ? Tziyun is a sign that there is a human bone here, so passersby and people who engage in Taharos will separate from it, until the Anshei Tamid will investigate and bury it. Perhaps before they bury it, a bone will be covered in earth or something else, or they will not see it. When they see the Tziyun, they will know that that there is a human bone here, take it and bury it in Gei Hamon Gog. All will be buried in one place. It will be a commemoration for the future, what Hashem did in it. The Tziyun will be one rock, or rocks gathered together.
Malbim: It is a sign to distance from it, both due to Tum'ah 2 and due to the plague. The miracle that the plague will not damage [Yisrael] will last only seven months. After this, people will build a Tziyun, and the buriers 3 will gather the bones to bury them in Gei Hamon Gog.
5a: Some learn from "v'Tamei Tamei Yikra" (Vayikra 13:45) ? Tum'ah calls, and tells people to separate.
Ohalos 2:3: A bone at least the size of a barley seed is Metamei one who moves or touches it, but not one who towers over it.
Why will the buriers not be concerned for the plague? Perhaps people who were already infected will bury them, or they will have special tools to take the bones without coming near them. (PF)
Why does it say "El Gei Hamon Gog"?
Radak: It means b'Gei Hamon Gog. Similarly, "v'El ha'Aron Titen Es ha'Edus" (Shemos 25:21) is like uva'Aron.
