Why did Hashem refer to the Neder that Yakov made in Beis-Eil on his way to Charan?
Rashi, Ramban and Rashbam: He was reminding Yakov that, having made the Neder - to turn the Matzeivah that he set up there into a House of G-d (to sacrifice on it), he was now obligated to fulfill it. 1
The Ramban refers to all the parts of the Neder that Yakov made in Beis-Eil (See above 28:20, 21).
Who said "Anochi ha'Keil Beis-Eil"?
Rashi (in Vayechi, 48:16) and Ramban: It was a Mal'ach 1 (though he did not say this at the same time as when he said "Sa Na Einecha u'Re'ei ... " - in Pasuk 11 - since there he was referring to the beginning of the six years, when Yakov began placing the sticks in the troughs; whereas here he is referring to the end of the six years, when Hashem instructed him to leave - which he did immediately - Ramban). 2
Ramban: He is synonymous with the Mal'ach ha'Go'el. See also Ramban DH 've'al Derech ha'Emes'.
Oznayim la'Torah: We can see from here Yakov's incredible humility, in that he did not tell Rachel and Le'ah about an angel appearing to him -until it came to the crunch and the time came for him to leave.
What does "Anochi ha'Keil Beis-Eil" mean?
Ramban (citing the Ibn Ezra and the R'dak): 'I am ha'Keol, Keil Beis-Eil - adding the word 'Keil'. 1
Why did Hashem say "Asher Mashachta"?
Rashbam: You were Makdish it, and you did not offer on it yet.
It said that an angel was speaking to Yakov. Why did he say "I am ha'Kel..."?
Tosfos ha'Shalem (2) #1: He should have said "so said Hashem."
Moshav Zekenim, Tosfos ha'Shalem (2) #2: Hashem created an image [that Nevi'im saw when He spoke to them]. It is called an angel.
Why did Hashem call himself "ha'Kel Beis Kel"?
Malbim: There I promised to guard you and return you, and you vowed