How did Betzalel implement the command to overlay the Aron on the inside and outside with gold?
Rashi: He actually constructed three Aronos, the basic one of Atzei Shitim according to the Torah's specifications, one that fitted plush inside it and one into which the middle one fitted plush.
What exactly was the "Zer Zahav"?
Rashi (in Tehilim, 139:3) : It is a Mechitzah (a wall) that surrounds.
Rashi in Eruvin, 4b explains that the Aron was nine Tefachim and the lid, one Tefach, in which case the outer golden Aron protruded a Tefach plus above the middle and inner Aronos
What is the significance of the Zer Zahav on the Aron?
Rashi: It symbolized the crown of Torah. 1
Da'as Zekenim. Moshav Zekenim - the Zerim on the Mizbe'ach and Shulchan, which symoblized the crowns of Kehunah and Malchus, respectively were taken by Aharon and David respectively. The crown of Torah, on the other hand, is open for anyone who wants to take it. "V'Asisa Alav" shows that Torah is the greatest of the three.
Seeing as there is no 'Yud' in the word "Zer", why is it ptonounced 'Zer' with a 'Tzeirei' and not 'Zar' witha 'Kamatz' or a 'Patach'?
Yoma, 72b: It teaches us that he meritous (to study Torah with positive intentions), it will be a crown (a Zir) for him; whereas if not (in the event that he studies it with negative intentions, it will be estranged from him. 1
See Torah Temimah, note 17.
Why did the Torah command to overlay the Aron with gold also on the inside? It is not seen!
Da'as Zekenim (citing Yoma 72b): This teaches that a Talmid-Chacham's inside must be like his outside. 1
Moshav Zekenim (37:1): They showed honor to the Aron. This teaches that one should honor Bnei Aniyim who learn Torah just like the wooden Aron was honored due to the Torah. The Aron corresponds to the Kisei ha'Kavod above - "Machon l'Shivtecha" (above, 15:17)! It was of wood, because the Torah is Etz Chayim (Mishlei 3:18).
Why did the Torah not command Moshe to make the Aron entirely of gold?
Da'as Zekenim: It would have been too heavy. Even though we say that the Aron carried those who carried it, that was a temporary occurrence. 1 However, if so, why was Uza punished (for going to catch the Aron, if normally it did not carry itself)? This requires investigation. Similarly, the Mizbechos were of wood and only plated with gold and copper, lest they be too heavy.
Refer to 5:11:151:1 and note.
I.e. we may not rely on miracles. If so, how could the outer covering of the Aron, which was Mashehu thick (Maharsha Yoma 72b), and of gold (which is soft), bear the weight of the Luchos? They carried the Aron via staves in rings welded onto the covering! Perhaps super-refined gold is strong. Shlomo made one Kikar of super-refined gold from 1000 Kikaros of gold (Menachos 29a). However, the total donation of gold for the Mishkan was less than 30 Kikar (38:24), and much was used for Kelim, plating the Kerashim