Why did Hashem find it necessary to promise Ya'akov that He would accompany him?
Rashi: Because he was afraid of Eisav and Lavan. 1
Tosfos ha'Shalem (4, citing Imrei No'am): Hashem promised only that they will not kill him. We find that Elifaz took his money!
What does "Ki Lo E'ezavcha" mean that is not contained in the preceding promises?
Rashi (in Pasuk 20): It means that Hashem would sustain Ya'akov. 1
Rashbam: It refers to Ya'akov on his travels, as a person who is traveling needs special protection. 2
Since this was the first time that Hashem spoke to Ya'akov, how could He state "asher Dibarti lach"?
Rashi #2 (in Bereishis 32:13): As in the previous explanation, it refers to the promise to Avraham that his children will be like the stars of the Heaven and the sand by the seashore (to which the Pasuk refers there, whereas here Hashem promised him that they would be like the dust of the earth).
Seforno: It refers to the earlier phrase " ... and you will spread out in all directions". Until that materializes, Hashem is assuring him that He will carry out all the promises in this Pasuk and that He will not forsake him.
Why does it say twice Asher - "Ad Asher Im Asisi Es Asher Dibarti Lach"?
Hadar Zekenim: This is an expression of a Shevu'ah Also Yakov said "Asher" twice in his vow.
רש"י: שהיה ירא מעשו ומלבן: מנין שהיה ירא מהם?
גור אריה: אם לא כן, למה הבטיחו ה' על כך יותר ממה שהבטיח לאבותיו.
רש"י: אם עשיתי - אם משמש בלשון כי: למה "אם" זה משמעו 'כי'?
גור אריה: בדרך כלל 'אם' משמעו ספק, אבל כאן לא היה ספק, ולכן פירש רש"י שזה מלשון 'אשר'.