כה תאמר לבני ישראל אהיה שלחני אליכם .ויאמר עוד אלקים אל משה כה תאמר אל בני ישראל יקוק אלקי אבתיכם אלקי אברהם אלקי יצחק ואלקי יעקב שלחני אליכם זה שמי לעלם וזה זכרי לדר דר.
After bringing the Ramban, Rabbeinu Yitzchak, the Rashbam, and the Baalei Tosfos, he says
הכוונה ברשב"ם ובבעלי התוס' בביאור אשר אהי' שהכוונה באהי' הי' אפשר לומר אלעתיד ולכך נתפרש: אשר אהי', שגם עכשיו בהוה אני במצב של אהי', כי אהי' בהוה זהו עומק פשוטו, וזהו קיצור שם יקו'ק אהי' בהוה וזהו יהי' בהוה
But we perceive events as taking place in sequence. In our experience, the future and the present are discrete. We cannot truly understand the divine perspective of simultaneity. Since it is impossible for humans to understand this, we cannot read the Name as it is written, but rather as we are capable of perceiving it, that of mastery and lordship. This is what the Gemara (Kiddushin 71a) means when it explains why in our passuk the word that is usually written לעולם is spelled without the vov, לעלם, by which the word "forever" acquires the additional implication of "hidden":
רבי אבינא רמי כתיב (שמות ג) זה שמי וכתיב (שמות ג) זה זכרי אמר הקב"ה לא כשאני נכתב אני נקרא נכתב אני ביו"ד ה"י ונקרא באל"ף דל"ת
But we have to ask, why davka now? What was the specific connection of this lesson to that moment in time?
Furthermore, in the beginning of this passuk Rashi (from Brachos 9b) says that Hashem told Moshe that in the future, there would be many other times of exile and suffering, and that even then Hashem would be with them:
אהיה אשר אהיה:אהיה עמם בצרה זו אשר אהיה עמם בשעבוד שאר מלכיות. אמר לפניו רבונו של עולם, מה אני מזכיר להם צרה אחרת דיים בצרה זו. אמר לו יפה אמרת, כה תאמר וגו'
Rav Bergman focuses on the relevance of this lesson to the issue of ידיעה ובחירה and the guilt of the Egyptians for enslaving the Jews. I want to offer a different interpretation.
I propose that temporary injustice is also unjust, but only if a moment exists as a separate entity. If the past and the future all exist simultaneously, then all events exist as a combination. If reality is not temporal, then the concept of temporary is meaningless. Momentary injustice is unjust, but if moments are not discrete entities, then examining a moment in isolation is an error.
Hashem was telling Moshe Rabbeinu that the harsh servitude of Mitzrayim is- and indeed must be- incomprehensible to Klal Yisrael. Yes, of course it stemmed from Avraham Avinu's words at the Bris bein habesarim, but it would seem that this was an extreme reaction to the act of an ancestor that lived al pi middas hadin and who had died many years before. Hashem said you should know that this is not the last time: there will be many such perplexing experiences for Klal Yisrael, and it will only be an awareness that Hashem's justice spans the past and the present and the future that will make it possible for them to comprehend, albeit as a matter of faith. After all, humans cannot truly understand what it means for all events to exist simultaneously. But at least if one does accept that postulate, the apparent injustice of an isolated moment loses its significance. Moments in time are not isolated. Taken as a whole, combining the cause and the effect and the innumerable intermediate steps, all is crystal clear.
In the comments, great unknown makes the point that such theology is a cold comfort to the suffering. I agree with him, and I realized that the way it's written, it sounds like the platitudes about omniscience and perfect knowledge and the millennia-long cycle of din v'cheshbon yielding results that our blinkered eyes cannot understand. That's not what I mean.
What I meant is this: I don't believe that life is an accounting book of debits and credits, where all that matters is whether at the end of the month there is a profit or a loss. A person that eats something that is extremely bitter is not helped by the fact that he later eats something else that is divinely sweet. A moment of injustice, a moment when the wicked torture the just and the innocent suffer is an injustice that is neither rectified nor mitigated by some future retribution to the sinner and reward to the saint. Contemplating the suffering of Mitzrayim, and looking forward to thousands of years of galus, Hashem told Moshe Rabbeinu that from the human perspective, it will have to appear that injustice is taking place. But at least we were taught that this apparent injustice is an artifact of our narrow experience of time as sequential and ephemeral. of our perception of each moment as an independent entity. But the deeper truth is that all the events we perceive as sequential and ephemeral exist simultaneously and irrevocably, and so there is no "moment" of injustice. The bitter and the sublime are both taking place together, and in the combination of all events, justice and good are absolute.