Exode 6:3

And I was revealed unto Abraham, and to Izhak, and to Jakob, as EI-Shaddai; but My Name Ye-ya, as it discovereth My Glory,* was not known to them. *Or, in the face of My Shekinah

“AND I APPEARED UNTO ABRAHAM, etc., BY THE NAME ‘E-IL SHA-DAI’ (G-D ALMIGHTY). I made many promises to him, and in all cases I said to him, I am G-d Almighty. BUT BY MY NAME, THE ETERNAL, WAS I NOT KNOWN UNTO THEM.” It was not written here, [“But My Name, the Eternal], I did not make known to them.” Rather, it is written, [But by My Name, the Eternal], was I not known unto them, meaning: “I was not recognized by them in My attribute of keeping faith, by reason of which My Name is called Eternal, which denotes that I am certain to fulfill the words [of My promise]. Indeed I made promises to the patriarchs but did not fulfill them [during their lifetime].”
All these are the words of Rashi. His intent is to explain that the fulfillment of His promise [to the patriarchs] had not taken place. Even though the time for the fulfillment had not arrived [in their lifetime, and consequently the absence of such fulfillment was no indication of a lack of His “keeping faith” since the time had not arrived], yet He was not known to the patriarchs in the fulfillment of His promise.
But with all this interpretation, Rashi has not properly explained the language of the text. (literally: and My Name the Eternal I was not made known to them). Ramban’s point is that according to Rashi’s interpretation, the verse should have read either (a) lo hodati (I did not make known), or (b) ush’mi Hashem lo noda lahem (and My Name the Eternal was not known to them). [According to his interpretation], it should be said, lo hodati [“and My Name, the Eternal, ‘I did not make known’ to them,” instead of lo nodati (I was not made known), as the text reads]. Or it should have said, “and My Name, the Eternal, lo noda (was not known) to them.” Perhaps according to Rashi’s opinion, the sense of the verse is: “and My Name is the Eternal, v’lo to the word lo — v’lo — thus making it independent of the expression ush’mi Hashem. Accordingly, there are two separate thoughts expressed: “and My Name is the Eternal,” which denotes that “I am certain to substantiate My promise,” and “I was not made known to them by that Name since I made promises to them but did not fulfill them.” nodati lahem,” meaning that “I was not made known to them by that Name.”

בא-ל שדי, a promise concerning the future that I have not yet fulfilled.

'ושמי ה, we have to explain the sequence as follows: “Although I have revealed Myself to the patriarchs as the attribute of Shaddai, My principal name, the one that represents My essence, etc.” We are faced with a repetition here, hence לא נודעתי להם, “I did not reveal Myself to the patriarchs as My principal attribute but only as My attribute Shaddai. But to you, Moses, I have revealed My principal attribute which I described as אהיה and זכרי ה'. In your lifetime I plan to fulfill My promise.”

לתת להם את ארץ כנען, to give the people the land of Canaan. The words ושמי ה' are connected to what was written at the beginning of the verse as I explained already. If the Torah had written הודעתי להם instead of נודעתי להם, the words ושמי ה' would have belonged to the statement לא הודעתי.

וארא, in a vision, a communication by G’d just below that of the level we know as נבואה, prophecy. Genesis 18,1 was one such example of G’d “appearing” to Avraham after his circumcision.

בא-ל שדי, by the attribute which demonstrates that I have created existence as such, as was pointed out in Genesis 17,1.

ושמי ה' לא נודעתי להם, the letter ב in the expression בא-ל שדי applies to the word ושמי. In effect what G’d is saying is that He has not made a point of becoming familiar to the patriarchs by His attribute Hashem when appearing to them, such as in the example mentioned. This was because He never experienced the need to change the laws of nature on their behalf. Seeing that the patriarchs could not have passed on knowledge about Me which I had not revealed to them, they in turn had not been able to pass on such knowledge to their children. I have to do this now in order to ensure that I can preserve the Children of Israel as My people.