Why does it say "Atem Edai"?
Rashi (9): You, Yisrael, testify that Hashem told Avraham of the exiles, and they came.
Radak: What I told you about Sancheriv - the evil that he did to you and his downfall - I told it all via a Navi before it was.
Malbim: Things told about Me, they are all true and lasting. This includes wonders that I did in the past - 600,000 saw with their eyes.
Who is Avdi, and what does the verse say about him?
Rashi: It is Yakov. He will testify that I promised to him when he went to Aram Naharayim, and I fulfilled it.
Radak: It is the Navi. Also he will testify that he said to you in My name, and as he said, so it was.
Radak citing Targum Yonasan: It is Mashi'ach, whom I desired.
Malbim: It is n the Navi. I showed the future to him as if it is the present, via a prophetic understanding that leaves no doubt.
Why does it say "Lema'an Ted'u"?
Rashi: I did all this so you will put your hearts to know Me.
Radak: From the first matters, you will know that the latter matters will be fulfilled, and I will fulfill My word, e.g. to take your children out of the last Galus.
Malbim: What Nevi'im say in My name, you know that it will be fulfilled, both via experience, and via tradition and Emunah.
Why does it say "v'Savinu Ki Ani Hu"?
Radak: You will understand that even if you did not have this testimony, from your Da'as you can understand that what I say is Emes, for I am Emes and My word is Emes.
Radak citing Ibn Ezra: I am the ultimate unity. Anything that exists, it is not 'Hu b'Atzmo 1 .'
I.e. it does not have intrinsic existence. It exists only due to Hashem's will. (PF)
What is the meaning of "Lefanai Lo Notzar Kel [v'Acharai Lo Yihyeh]"?
Radak: This was difficult for the Meforshim, for it says Lefanai and Acharai. Hashem has no beginning or end! Also, it says Notzar (as if Kel was formed)! Some say that before I formed beings with forms, no god other than Me formed anything. Also after I formed beings, no idol formed anything.
Radak citing his father: Notzar is Samuch to Kel, for there is a Patach under the Tzadi. Nothing was formed by a god other than Me, and nothing will be formed via any other god afterwards. I.e. after they were formed via Me, nothing will be formed via any god.
Malbim: The early idolaters attributed fathers and children to their gods, and said that this god fought with his father and demoted him from divinity, and closed him in the depths and ruled in place of him in Shamayim, until his son did so to him. I am different - no god was formed before Me, and I did not inherit My Elokus from another, and no one will rule after Me.