Why is the 'Yud' missing from "Va'ashlichem"?
Ba'al ha'Turim (citing the Yerushalmi in Ta'anis, 4:5): To teach us the Yud (Aseres ha')Dibros flew out of the Luchos (and the Luchos became too heavy for Moshe to hold, and they fell).
Why did Moshe insert the breaking of the Luchos here?
Ramban #1: As part of the series of sins for which Moshe is rebuking Yisrael, he is pointing out the severity of the Chet ha'Eigel, to the point that, when he saw the people rejoicing before the Calf, he could not restrain himself from breaking the Luchos. 1
Ramban #2: To inform them how he had been Moser Nefesh on their behalf, by breaking the (Divinely-written) Luchos for their good. 2
Ramban: On any event it was necessary to mention it, in order to tell them about the second Luchos (at the beginning of chapter 10).
Ramban (citing Midrash Rabah), Da'as Zekenim (16), Rosh (16): 'It is better for them to be judged as 'a single girl' (by destroying their Kesubah) who was Mezanah, than as 'a married woman.' (And Hashem thanked Moshe for breaking the Luchos. See the last Rashi in the Torah and Targum Yonasan later on 10:1).
Why does the Torah insert the phrase "Va'espos b'Shenei Luchos" - bearing in mind that he was already holding them?
Or ha'Chayim: Initially, the Luchos held themselves, 1 and it is only when they came in the vicinity of the Eigel that Moshe needed to grab hold of them to stop them from falling.
Moshe needed to hold on to them firmly in order to hurl them down with force and smash them. 2 (EC)
Rosh (16): Hashem was holding two Tefachim of the Luchos, Moshe held Tefachim on the other end, and two Tefachim were in the middle (Shemos Rabah 47:6). Moshe seized them and broke them.
Alshich: Before Chet ha'Egel, the Luchos were so spiritual that it was almost not applicable to discuss 'holding' them.
Ha'Kesav veha'Kabalah #1: Initially, when Hashem told Moshe to descend, he thought to leave the Luchos above. He reconsidered, and took them to break them in front of them, to inform them what they lost.
Ha'Kesav veha'Kabalah #2, citing Avos d'R. Nasan (2): When Moshe saw the Egel, he turned back. The 70 Zekenim saw the Luchos, and ran and held onto one end of them. 3 Moshe overpowered them and took them from their grasp.
RS"R Hirsh: Initially, Moshe was a mere carrier of the treasure deposited with him. Now he seized them to do what he decided to do with them (break them).
Ha'Emek Davar: Initially they were on Moshe's hands. Now, miraculously, Hashem enabled him to grab them and break them. This shows that Hashem was not concerned to save these precious Luchos!
As the Torah indicates n Pasuk 15, where it writes "u'Shnei Luchos ha'Bris Al Shtei Yadai".
Unlike the Yerushalmi, which explains that the letters that were engraved on the Luchos made them lighter and enabled Moshe to carry them, and that, when the letters flew away, they became too heavy for him to hold and he dropped them. The word "va'Ashabrem" however, implies that he threw them down forcefully. (EC) Perhaps Moshe could not hold them up, but he was able to propel them towards Yisrael, so they would see them break