Why did Hashem add the word "Na"?
Rashi: He was pleading with Avraham to pass this last (and most difficult) of all the ten tests, so that people should not belittle his achievement in passing the first nine. 1
Targum Onkelos and Targum Yonasan: "Na" actually means (not 'please', but) 'now'.
Even though in fact, it was a test for Yitzchak as well
Seeing as there was only one Yitzchak, why did Hashem see fit to add "es Bincha" and "es Yechidcha?
Rashi #1: In order to soften the impact. Had He told him directly, people would have said that Avraham only obeyed Hashem because he was confused. 1
Rashi #2: To make sure that he got the message loud and clear, thereby endearing the Mitzvah on him.
Rashi #3: Bearing in mind that every word that Avraham spoke was in the service of Hashem, and therefore earned him reward, Hashem wanted to add to his reward, by commenting that he had two sons and that each one was an only son to his mother - before finally concluding "Yitzchak". 2
Ramban: Hashem was stressing that Yitzchak was not only his son (whom every father loves dearly), but the son of his main wife Sarah, who alone was called 'Zera' - to magnify the Mitzvah and to increase his reward.
Why is Yerushalayim referred to as 'Eretz ha'Moriyah'?
Rashi #1: Because Hora'ah (P'sak Halachah) was destined to go out from Yerushalayim. 1
Targum Onkelos (according to Rashi) 2 : 'The land of Avodas Hashem' - with reference to the Ketores (the most beloved of all the Korbanos [whose first ingredient was 'Mor']) which Yisrael would later offer in Yerushalayim.
Targum Onkelos (according to the Ramban #1): The location where people worshipped Hashem. 3 In that case, "Moriyah" stems from the word "Mora" - where they feared Hashem and sacrificed to Him.
Ramban #2: It was called by that name because the precious spice Mor (myrrh) grew there.
Rashbam: It is missing an 'Alef', 4 and means simply 'the Land of the Emori'
Because Beis-Din ha'Gadol sat in the LIshkas ha'Gazis in the Beis-Hamikdash..
The Ramban cites this in the name of the Bereishis Rabah, which in turn, bases it on the Pasuk in Shir ha'Shirim, (4:6) which refers to Yerushalayim as "Har ha'Mor".
With reference to Pirkei de'Rebbi Eliezer - that Hashem showed Avraham the Mizbe'ach (on which Adam, Kayin and Hevel and No'ach sacrificed), which was located there. Refer to 22:9:1:1
What was the greatest aspect of the test?
Rashi (Va'eira, Sh'mos 6:1): In spite of Hashem having promised him "Ki be'Yitzchak Yikarei L'cha Zara", Avraham did not query Him when He now ordered him to bring him up as an Olah.
Having promised Avraham that his seed will be called through Yitzchak, how could Hashem now order him to bring him up as an Olah?
Rashi (Pasuk 12): Hashem did not command him to sacrifice Yitzchak, but to bring him up [on a Mizbe'ach] as an Olah, and it was Avraham who jumped to the wrong conclusion. Having brought him up, Hashem then ordered him to take him down. 1
Why did Hashem choose specifically Har ha'Moriyah for the Akeidah?
Ramban #1: So that the merit of the Akeidah would be permanently attached to the Mountain on which the Beis-Hamikdash would be built.
Ramban #2: Because it was three days journey from where Avraham lived. Had Hashem ordered him to bring up Yitzchak immediately, people would have said that he was confused. 1