Posted on 02/23/19
Moshe Rabbeinu, in his defence of B'nei Yisrael, pleads with HaShem (32:13) to "remember Avraham, Yitzchak and Yaakov to whom You vowed by Your Self..." Rashi explains Moshe's plea. "You did not swear to them by something that is perishable and impermanent, not by the heavens, not by the earth; not by the mountains and not by the hills, but by Your Self."
Rashi to Devarim 32:1 explains that when Moshe Rabbeinu gave B'nei Yisrael their final discourse, the song of Ha'azinu, he made the heavens and the earth the witnesses for he will ultimately pass from this world but the heavens and the earth are everlasting. With these two Rashis presented beside each other, the difficulty is rather obvious. Here the heavens and earth are considered to be passing entities with no lasting life and suddenly, in Devarim, they become eternal.
I found a simple, practical answer in the Silberman Chumash. In Devarim, the heavens and earth are being compared to Man. They are surely more everlasting than Man. However, here they are being compared to HaShem, who is surely far more everlasting than the heavens and the earth. (Another reader has pointed out that heaven and earth are chosen to serve as witnesses against Man. But here, their task would have been to hold HaShem accountable, for which they would be inadequate.)
Perhaps another way to resolve this discrepancy is that the heavens and earth may very well be eternal, everlasting entities from a practical perspective. However, what Moshe is saying here is that their very existence is at the whim of HaShem's will. Although in all likelihood they will never cease to be, they very well could if HaShem so desired. And that lends a special significance to the fact that HaShem swore by His very Self to Avraham, Yitzchak and Yaakov.