What is the significance of the word "Lachein"?
Rashi #1: Based on the Shevu'ah mentioned in the previous Pasuk, Hashem would now set in motion the process of redemption. 1
Rashi #2 (in Yechezkel): Lachein is itself a Lashon of Shevu'ah.
Seforno: For the three reasons mentioned earlier, 2 Moshe should inform Yisrael that He, the Creator of the whole of existence, would take them out of Egypt, changing some of the laws of nature in the process.
What is the significance of the statement "Ani Hashem"?
Rashi and Rashbam (based on Pasuk 3): To inform Yisrael that Hashem was now about to fulfill His promise.
What is the significance of the four expressions mentioned in this Pasuk and in Pasuk 7?
Ramban: They pertain to the four 1 stages of the Ge'ulah: 1. That Hashem would take them out of Egypt; 2. That even whilst they still there, the Egyptians would have no more jurisdiction over them to make them work; 3. That He would serve the Egyptians a series of punishments until they offered Yisrael to Him as a redemption of their souls; 2 4. That Hashem will take Yisrael as His treasured nation 3 - when they came to Har Sinai to receive the Torah.
Seforno: They pertain to the four stages of the Ge'ulah: (a) The moment the plagues began the slavery came to an end; (b) When, on the fifteenth of Nisan, they gathered in Ra'amses to leave Egypt, they were considered rescued; (c) The drowning of Egyptians in the Yam-Suf was the completion of the redemption; 4 (d) When Yisrael received the Torah at Har Sinai.
Ba'al ha'Turim: They also signify the four redemptions (from the four nations who would later render them subservient (Bavel. Madai, Greece and Rome). 5
Hadar Zekenim: V'Heveisi is not counted, for it is not an expression of Ge'ulah. Even so, it is a source for a fifth cup of wine at the Seder. Divrei Eliyahu - it is called the Kos of Eliyahu, for it is a Safek whether or not it is needed, and Eliyahu will resolve this and all other Sefekos.
Since the term Ge'ulah is a form of sale (Ramban).
As the Torah says in Yisro (19:5 [Ramban]).
Seforno: As the Torah writes in Beshalach (14:30). This is because they were no longer considered 'fleeing slaves'.
The four cups of wine that we drink at the Seder also correspond to the four expressions of Ge'ulah (Rashi, Pesachim, 99b). See also Ba'al ha'Turim
And what is the significance of the words "u'vi'Zero'a Netuyah"?
Ramban: It teaches us that Hashem's Hand remained outstretched (to strike them again and again, each time they refused) until He took us out of Egypt.
Targum Onkelos and Targum Yonasan: It means that Hashem dealt the Egyptians many punishments.