How could Moshe place the jar of Manna in front of the Aron, "Lifnei Hashem" (see Sifsei Chachamim]), seeing as the Mishkan with its Keilim had not yet been built?
Rashi and Rashbam: This Pasuk was actually said only after the Mishkan had been built, and it inserts it here 1 because it belongs to the Parshah of Manna.
In keeping with the principle 'Ein Mukdam u'Me'uchar ba'Torah.'
What is the definition of "Tzintzenes"?
Rashi (citing the Mechilta and Targum Onkelos) and Targum Yonasan: It is an earthenware jar. 1
Mechilta: It is a glass jar 2 - which is the only material through which one see.
Why does the Torah insert the unusual word "v'Sen Shamah Melo ha'Omer ... " (See Torah Temimah, note 53)?
Yoma 52b: To teach us via a Gezerah Shavah "Shamah" "Shamah" to Parshas Ki Sisa (30:36), in connection with the Aron, that the jar of Mann, like the Aron, was hidden.
What is the Torah referring to when it writes, "Lifnei Hashem" in this Pasuk; and "Lifnei ha'Eidus" in the next (16:34)?
Rashi and Rashbam: Both Pesukim are referring to the Aron ha'Kodesh - after the Mishkan was built. 1
QUESTIONS ON RASHI
Rashi writes: "Tzintzenes - an earthenware flask." Why need Rashi tell us this?
Gur Aryeh: The doubled root (Tzadi-Nun-Tzadi-Nun) indicates that the word "Tzintzenes" is not merely a name; rather, it has some inherent meaning. 1 Root "Tzadi-Nun-Nun" means 'to cool down;' the function of this type of flask was to cool down its contents, facilitating their preservation. 2
Gur Aryeh: That is why, out of the hundreds of names of places mentioned in Sefer Yehoshua, the Gemara (Gitin 7a) expounds upon only those names that are doubled - such as "Ad'adah" and "Sansanah" (Yehoshua 15:22,31).
Compare to Yirmeyahu 32:14. (The Torah Temimah (note 52) points out, that the Vilna Gaon's text in the Mechilta is "glassware", rather than "earthenware" - i.e., a utensil that one can see through (Meitzitz).)